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 $223.43   13.121%   $252.7463   $252.75   $252.75   $252.70  
  Purchase #2 $243.45   3.323%   $251.5398   $251.54   $251.55   $251.50  
  Purchase #3 $126.63   10.523%   $139.9553   $139.96   $139.95   $140.00  
  Purchase #4 $41.79   11.432%   $46.5674   $46.57   $46.55   $46.60  
  Purchase #5 $62.94   11.853%   $70.4003   $70.40   $70.40   $70.40  
  Purchase #6 $100.84   13.816%   $114.7721   $114.77   $114.75   $114.80  
  Purchase #7 $24.64   8.428%   $26.7167   $26.72   $26.70   $26.70  
  7 purchase totals = $823.72       $902.6979   $902.71   $902.65   $902.70