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 $75.76   11.622%   $84.5648   $84.56   $84.55   $84.60  
  Purchase #2 $89.92   7.681%   $96.8268   $96.83   $96.85   $96.80  
  Purchase #3 $87.90   6.227%   $93.3735   $93.37   $93.35   $93.40  
  Purchase #4 $184.53   9.497%   $202.0548   $202.05   $202.05   $202.10  
  Purchase #5 $203.72   11.426%   $226.997   $227.00   $227.00   $227.00  
  Purchase #6 $18.71   8.567%   $20.3129   $20.31   $20.30   $20.30  
  Purchase #7 $185.53   12.411%   $208.5561   $208.56   $208.55   $208.60  
  7 purchase totals = $846.07       $932.6859   $932.68   $932.65   $932.80