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 $232.90   6.137%   $247.1931   $247.19   $247.20   $247.20  
  Purchase #2 $101.61   13.718%   $115.5489   $115.55   $115.55   $115.50  
  Purchase #3 $62.81   3.821%   $65.21   $65.21   $65.20   $65.20  
  Purchase #4 $37.64   4.151%   $39.2024   $39.20   $39.20   $39.20  
  Purchase #5 $32.48   10.118%   $35.7663   $35.77   $35.75   $35.80  
  Purchase #6 $182.33   13.532%   $207.0029   $207.00   $207.00   $207.00  
  Purchase #7 $236.49   9.322%   $258.5356   $258.54   $258.55   $258.50  
  7 purchase totals = $886.26       $968.4592   $968.46   $968.45   $968.40