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 $169.30   13.648%   $192.4061   $192.41   $192.40   $192.40  
  Purchase #2 $221.54   6.510%   $235.9623   $235.96   $235.95   $236.00  
  Purchase #3 $145.34   6.325%   $154.5328   $154.53   $154.55   $154.50  
  Purchase #4 $42.56   12.735%   $47.98   $47.98   $48.00   $48.00  
  Purchase #5 $225.66   9.804%   $247.7837   $247.78   $247.80   $247.80  
  Purchase #6 $91.83   5.546%   $96.9229   $96.92   $96.90   $96.90  
  Purchase #7 $125.63   8.525%   $136.34   $136.34   $136.35   $136.30  
  7 purchase totals = $1,021.86       $1,111.9278   $1,111.92   $1,111.95   $1,111.90