Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $92.85   12.655%   $104.6002   $104.60   $104.60   $104.60  
  Purchase #2 $208.78   13.729%   $237.4434   $237.44   $237.45   $237.40  
  Purchase #3 $162.77   13.549%   $184.8237   $184.82   $184.80   $184.80  
  Purchase #4 $113.65   6.237%   $120.7384   $120.74   $120.75   $120.70  
  Purchase #5 $168.60   4.195%   $175.6728   $175.67   $175.65   $175.70  
  Purchase #6 $92.40   8.767%   $100.5007   $100.50   $100.50   $100.50  
  Purchase #7 $175.91   13.547%   $199.7405   $199.74   $199.75   $199.70  
  7 purchase totals = $1,014.96       $1,123.5197   $1,123.51   $1,123.50   $1,123.40