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 $47.61   7.163%   $51.0203   $51.02   $51.00   $51.00  
  Purchase #2 $83.68   13.253%   $94.7701   $94.77   $94.75   $94.80  
  Purchase #3 $150.58   7.374%   $161.6838   $161.68   $161.70   $161.70  
  Purchase #4 $244.99   7.721%   $263.9057   $263.91   $263.90   $263.90  
  Purchase #5 $35.88   11.863%   $40.1364   $40.14   $40.15   $40.10  
  Purchase #6 $189.71   11.289%   $211.1264   $211.13   $211.15   $211.10  
  Purchase #7 $133.36   10.109%   $146.8414   $146.84   $146.85   $146.80  
  7 purchase totals = $885.81       $969.4841   $969.49   $969.50   $969.40