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 $81.65   3.151%   $84.2228   $84.22   $84.20   $84.20  
  Purchase #2 $203.49   11.441%   $226.7713   $226.77   $226.75   $226.80  
  Purchase #3 $236.82   3.788%   $245.7907   $245.79   $245.80   $245.80  
  Purchase #4 $229.64   6.867%   $245.4094   $245.41   $245.40   $245.40  
  Purchase #5 $55.43   5.347%   $58.3938   $58.39   $58.40   $58.40  
  Purchase #6 $249.29   5.354%   $262.637   $262.64   $262.65   $262.60  
  Purchase #7 $121.70   13.465%   $138.0869   $138.09   $138.10   $138.10  
  7 purchase totals = $1,178.02       $1,261.3119   $1,261.31   $1,261.30   $1,261.30