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 $168.62   8.137%   $182.3406   $182.34   $182.35   $182.30  
  Purchase #2 $170.94   13.485%   $193.9913   $193.99   $194.00   $194.00  
  Purchase #3 $99.90   9.569%   $109.4594   $109.46   $109.45   $109.50  
  Purchase #4 $239.67   6.418%   $255.052   $255.05   $255.05   $255.10  
  Purchase #5 $179.79   5.796%   $190.2106   $190.21   $190.20   $190.20  
  Purchase #6 $218.63   5.686%   $231.0613   $231.06   $231.05   $231.10  
  Purchase #7 $236.72   13.804%   $269.3968   $269.40   $269.40   $269.40  
  7 purchase totals = $1,314.27       $1,431.5120   $1,431.51   $1,431.50   $1,431.60