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 $161.82   13.550%   $183.7466   $183.75   $183.75   $183.70  
  Purchase #2 $229.97   9.441%   $251.6815   $251.68   $251.70   $251.70  
  Purchase #3 $243.33   11.567%   $271.476   $271.48   $271.50   $271.50  
  Purchase #4 $187.58   11.689%   $209.5062   $209.51   $209.50   $209.50  
  Purchase #5 $92.63   13.803%   $105.4157   $105.42   $105.40   $105.40  
  Purchase #6 $210.49   3.287%   $217.4088   $217.41   $217.40   $217.40  
  Purchase #7 $72.90   10.127%   $80.2826   $80.28   $80.30   $80.30  
  7 purchase totals = $1,198.72       $1,319.5174   $1,319.53   $1,319.55   $1,319.50