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 $50.93   9.833%   $55.9379   $55.94   $55.95   $55.90  
  Purchase #2 $219.90   8.139%   $237.7977   $237.80   $237.80   $237.80  
  Purchase #3 $34.43   6.565%   $36.6903   $36.69   $36.70   $36.70  
  Purchase #4 $101.35   9.831%   $111.3137   $111.31   $111.30   $111.30  
  Purchase #5 $91.95   8.370%   $99.6462   $99.65   $99.65   $99.60  
  Purchase #6 $50.78   10.288%   $56.0042   $56.00   $56.00   $56.00  
  Purchase #7 $183.94   12.554%   $207.0318   $207.03   $207.05   $207.00  
  7 purchase totals = $733.28       $804.4218   $804.42   $804.45   $804.30