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 $32.32   11.516%   $36.042   $36.04   $36.05   $36.00  
  Purchase #2 $56.61   8.387%   $61.3579   $61.36   $61.35   $61.40  
  Purchase #3 $204.30   8.201%   $221.0546   $221.05   $221.05   $221.10  
  Purchase #4 $109.73   11.761%   $122.6353   $122.64   $122.65   $122.60  
  Purchase #5 $53.80   8.549%   $58.3994   $58.40   $58.40   $58.40  
  Purchase #6 $148.25   5.181%   $155.9308   $155.93   $155.95   $155.90  
  Purchase #7 $186.47   8.342%   $202.0253   $202.03   $202.05   $202.00  
  7 purchase totals = $791.48       $857.4453   $857.45   $857.50   $857.40