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 $235.71   11.631%   $263.1254   $263.13   $263.15   $263.10  
  Purchase #2 $192.73   9.155%   $210.3744   $210.37   $210.35   $210.40  
  Purchase #3 $12.87   6.596%   $13.7189   $13.72   $13.70   $13.70  
  Purchase #4 $59.61   9.260%   $65.1299   $65.13   $65.15   $65.10  
  Purchase #5 $202.69   5.175%   $213.1792   $213.18   $213.20   $213.20  
  Purchase #6 $33.76   6.648%   $36.0044   $36.00   $36.00   $36.00  
  Purchase #7 $139.65   13.708%   $158.7932   $158.79   $158.80   $158.80  
  7 purchase totals = $877.02       $960.3254   $960.32   $960.35   $960.30