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 $70.51   12.527%   $79.3428   $79.34   $79.35   $79.30  
  Purchase #2 $157.58   11.485%   $175.6781   $175.68   $175.70   $175.70  
  Purchase #3 $156.30   12.381%   $175.6515   $175.65   $175.65   $175.70  
  Purchase #4 $9.83   11.485%   $10.959   $10.96   $10.95   $11.00  
  Purchase #5 $224.66   9.824%   $246.7306   $246.73   $246.75   $246.70  
  Purchase #6 $199.38   4.300%   $207.9533   $207.95   $207.95   $208.00  
  Purchase #7 $158.43   5.165%   $166.6129   $166.61   $166.60   $166.60  
  7 purchase totals = $976.69       $1,062.9282   $1,062.92   $1,062.95   $1,063.00