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 $207.61   8.220%   $224.6755   $224.68   $224.70   $224.70  
  Purchase #2 $244.87   9.702%   $268.6273   $268.63   $268.65   $268.60  
  Purchase #3 $60.45   12.689%   $68.1205   $68.12   $68.10   $68.10  
  Purchase #4 $179.68   12.431%   $202.016   $202.02   $202.00   $202.00  
  Purchase #5 $244.86   7.786%   $263.9248   $263.92   $263.90   $263.90  
  Purchase #6 $219.66   8.252%   $237.7863   $237.79   $237.80   $237.80  
  Purchase #7 $232.87   6.737%   $248.5585   $248.56   $248.55   $248.60  
  7 purchase totals = $1,390.00       $1,513.7089   $1,513.72   $1,513.70   $1,513.70