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 $113.59   11.444%   $126.5892   $126.59   $126.60   $126.60  
  Purchase #2 $60.37   10.535%   $66.73   $66.73   $66.75   $66.70  
  Purchase #3 $179.46   11.185%   $199.5326   $199.53   $199.55   $199.50  
  Purchase #4 $240.82   10.426%   $265.9279   $265.93   $265.95   $265.90  
  Purchase #5 $85.98   9.621%   $94.2521   $94.25   $94.25   $94.30  
  Purchase #6 $192.67   13.581%   $218.8365   $218.84   $218.85   $218.80  
  Purchase #7 $158.93   7.471%   $170.8037   $170.80   $170.80   $170.80  
  7 purchase totals = $1,031.82       $1,142.6720   $1,142.67   $1,142.75   $1,142.60