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 $29.27   10.791%   $32.4285   $32.43   $32.45   $32.40  
  Purchase #2 $194.89   13.461%   $221.1241   $221.12   $221.10   $221.10  
  Purchase #3 $75.43   7.207%   $80.8662   $80.87   $80.85   $80.90  
  Purchase #4 $162.31   13.593%   $184.3728   $184.37   $184.35   $184.40  
  Purchase #5 $250.28   10.581%   $276.7621   $276.76   $276.75   $276.80  
  Purchase #6 $174.50   3.836%   $181.1938   $181.19   $181.20   $181.20  
  Purchase #7 $137.56   7.769%   $148.247   $148.25   $148.25   $148.20  
  7 purchase totals = $1,024.24       $1,124.9945   $1,124.99   $1,124.95   $1,125.00