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 $246.60   10.123%   $271.5633   $271.56   $271.55   $271.60  
  Purchase #2 $208.26   11.732%   $232.6931   $232.69   $232.70   $232.70  
  Purchase #3 $151.87   13.323%   $172.1036   $172.10   $172.10   $172.10  
  Purchase #4 $158.67   11.672%   $177.19   $177.19   $177.20   $177.20  
  Purchase #5 $43.88   5.115%   $46.1245   $46.12   $46.10   $46.10  
  Purchase #6 $36.95   9.652%   $40.5164   $40.52   $40.50   $40.50  
  Purchase #7 $215.86   7.721%   $232.5266   $232.53   $232.55   $232.50  
  7 purchase totals = $1,062.09       $1,172.7175   $1,172.71   $1,172.70   $1,172.70