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 $113.84   11.336%   $126.7449   $126.74   $126.75   $126.70  
  Purchase #2 $71.91   12.572%   $80.9505   $80.95   $80.95   $81.00  
  Purchase #3 $5.83   3.661%   $6.0434   $6.04   $6.05   $6.00  
  Purchase #4 $216.45   9.843%   $237.7552   $237.76   $237.75   $237.80  
  Purchase #5 $178.86   4.292%   $186.5367   $186.54   $186.55   $186.50  
  Purchase #6 $196.56   6.343%   $209.0278   $209.03   $209.05   $209.00  
  Purchase #7 $151.46   5.189%   $159.3193   $159.32   $159.30   $159.30  
  7 purchase totals = $934.91       $1,006.3778   $1,006.38   $1,006.40   $1,006.30