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 $54.46   11.257%   $60.5906   $60.59   $60.60   $60.60  
  Purchase #2 $135.94   4.311%   $141.8004   $141.80   $141.80   $141.80  
  Purchase #3 $182.51   3.332%   $188.5912   $188.59   $188.60   $188.60  
  Purchase #4 $210.57   9.186%   $229.913   $229.91   $229.90   $229.90  
  Purchase #5 $60.52   4.370%   $63.1647   $63.16   $63.15   $63.20  
  Purchase #6 $225.42   10.353%   $248.7577   $248.76   $248.75   $248.80  
  Purchase #7 $72.53   10.450%   $80.1094   $80.11   $80.10   $80.10  
  7 purchase totals = $941.95       $1,012.9270   $1,012.92   $1,012.90   $1,013.00