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 $243.92   8.211%   $263.9483   $263.95   $263.95   $263.90  
  Purchase #2 $158.79   4.351%   $165.699   $165.70   $165.70   $165.70  
  Purchase #3 $23.56   8.203%   $25.4926   $25.49   $25.50   $25.50  
  Purchase #4 $7.31   13.470%   $8.2947   $8.29   $8.30   $8.30  
  Purchase #5 $250.34   5.282%   $263.563   $263.56   $263.55   $263.60  
  Purchase #6 $54.36   6.292%   $57.7803   $57.78   $57.80   $57.80  
  Purchase #7 $224.25   5.785%   $237.2229   $237.22   $237.20   $237.20  
  7 purchase totals = $962.53       $1,022.0008   $1,021.99   $1,022.00   $1,022.00