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 $237.65   6.288%   $252.5934   $252.59   $252.60   $252.60  
  Purchase #2 $241.90   12.331%   $271.7287   $271.73   $271.75   $271.70  
  Purchase #3 $216.47   8.432%   $234.7228   $234.72   $234.70   $234.70  
  Purchase #4 $100.87   9.499%   $110.4516   $110.45   $110.45   $110.50  
  Purchase #5 $195.29   13.387%   $221.4335   $221.43   $221.45   $221.40  
  Purchase #6 $44.32   11.591%   $49.4571   $49.46   $49.45   $49.50  
  Purchase #7 $56.99   5.597%   $60.1797   $60.18   $60.20   $60.20  
  7 purchase totals = $1,093.49       $1,200.5668   $1,200.56   $1,200.60   $1,200.60