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 $224.83   9.688%   $246.6115   $246.61   $246.60   $246.60  
  Purchase #2 $100.31   8.226%   $108.5615   $108.56   $108.55   $108.60  
  Purchase #3 $173.60   6.507%   $184.8962   $184.90   $184.90   $184.90  
  Purchase #4 $148.65   12.672%   $167.4869   $167.49   $167.50   $167.50  
  Purchase #5 $159.43   9.653%   $174.8198   $174.82   $174.80   $174.80  
  Purchase #6 $61.55   4.345%   $64.2243   $64.22   $64.20   $64.20  
  Purchase #7 $208.82   10.514%   $230.7753   $230.78   $230.80   $230.80  
  7 purchase totals = $1,077.19       $1,177.3755   $1,177.38   $1,177.35   $1,177.40