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 $83.75   13.327%   $94.9114   $94.91   $94.90   $94.90  
  Purchase #2 $62.44   13.565%   $70.91   $70.91   $70.90   $70.90  
  Purchase #3 $23.36   8.529%   $25.3524   $25.35   $25.35   $25.40  
  Purchase #4 $245.75   12.308%   $275.9969   $276.00   $276.00   $276.00  
  Purchase #5 $93.73   12.329%   $105.286   $105.29   $105.30   $105.30  
  Purchase #6 $33.32   7.372%   $35.7764   $35.78   $35.80   $35.80  
  Purchase #7 $119.36   7.709%   $128.5615   $128.56   $128.55   $128.60  
  7 purchase totals = $661.71       $736.7946   $736.80   $736.80   $736.90