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 $50.37   11.593%   $56.2094   $56.21   $56.20   $56.20  
  Purchase #2 $84.78   13.662%   $96.3626   $96.36   $96.35   $96.40  
  Purchase #3 $247.79   10.469%   $273.7311   $273.73   $273.75   $273.70  
  Purchase #4 $68.71   12.576%   $77.351   $77.35   $77.35   $77.40  
  Purchase #5 $57.39   3.300%   $59.2839   $59.28   $59.30   $59.30  
  Purchase #6 $124.87   9.203%   $136.3618   $136.36   $136.35   $136.40  
  Purchase #7 $32.94   4.320%   $34.363   $34.36   $34.35   $34.40  
  7 purchase totals = $666.85       $733.6628   $733.65   $733.65   $733.80