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 $208.76   12.180%   $234.187   $234.19   $234.20   $234.20  
  Purchase #2 $97.29   11.499%   $108.4774   $108.48   $108.50   $108.50  
  Purchase #3 $234.79   4.495%   $245.3438   $245.34   $245.35   $245.30  
  Purchase #4 $131.28   4.781%   $137.5565   $137.56   $137.55   $137.60  
  Purchase #5 $65.64   11.710%   $73.3264   $73.33   $73.35   $73.30  
  Purchase #6 $47.41   12.857%   $53.5055   $53.51   $53.50   $53.50  
  Purchase #7 $206.65   12.381%   $232.2353   $232.24   $232.25   $232.20  
  7 purchase totals = $991.82       $1,084.6319   $1,084.65   $1,084.70   $1,084.60