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 $46.95   11.351%   $52.2793   $52.28   $52.30   $52.30  
  Purchase #2 $198.57   10.607%   $219.6323   $219.63   $219.65   $219.60  
  Purchase #3 $138.57   13.745%   $157.6164   $157.62   $157.60   $157.60  
  Purchase #4 $38.71   5.874%   $40.9838   $40.98   $41.00   $41.00  
  Purchase #5 $21.90   7.258%   $23.4895   $23.49   $23.50   $23.50  
  Purchase #6 $196.43   8.823%   $213.761   $213.76   $213.75   $213.80  
  Purchase #7 $82.78   3.833%   $85.953   $85.95   $85.95   $86.00  
  7 purchase totals = $723.91       $793.7153   $793.71   $793.75   $793.80