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 $60.44   9.820%   $66.3752   $66.38   $66.40   $66.40  
  Purchase #2 $160.96   12.276%   $180.7194   $180.72   $180.70   $180.70  
  Purchase #3 $173.92   11.263%   $193.5086   $193.51   $193.50   $193.50  
  Purchase #4 $81.75   4.749%   $85.6323   $85.63   $85.65   $85.60  
  Purchase #5 $96.36   4.764%   $100.9506   $100.95   $100.95   $101.00  
  Purchase #6 $235.60   3.483%   $243.8059   $243.81   $243.80   $243.80  
  Purchase #7 $16.99   12.119%   $19.049   $19.05   $19.05   $19.00  
  7 purchase totals = $826.02       $890.0410   $890.05   $890.05   $890.00