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 $53.54   10.105%   $58.9502   $58.95   $58.95   $59.00  
  Purchase #2 $208.73   7.598%   $224.5893   $224.59   $224.60   $224.60  
  Purchase #3 $65.40   10.452%   $72.2356   $72.24   $72.25   $72.20  
  Purchase #4 $139.96   9.146%   $152.7607   $152.76   $152.75   $152.80  
  Purchase #5 $7.57   13.106%   $8.5621   $8.56   $8.55   $8.60  
  Purchase #6 $246.50   13.217%   $279.0799   $279.08   $279.10   $279.10  
  Purchase #7 $143.56   7.159%   $153.8375   $153.84   $153.85   $153.80  
  7 purchase totals = $865.26       $950.0153   $950.02   $950.05   $950.10