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 $51.66   13.781%   $58.7793   $58.78   $58.80   $58.80  
  Purchase #2 $177.52   5.845%   $187.896   $187.90   $187.90   $187.90  
  Purchase #3 $58.74   8.723%   $63.8639   $63.86   $63.85   $63.90  
  Purchase #4 $240.73   11.710%   $268.9195   $268.92   $268.90   $268.90  
  Purchase #5 $124.51   13.207%   $140.954   $140.95   $140.95   $141.00  
  Purchase #6 $243.73   10.126%   $268.4101   $268.41   $268.40   $268.40  
  Purchase #7 $236.85   4.227%   $246.8616   $246.86   $246.85   $246.90  
  7 purchase totals = $1,133.74       $1,235.6844   $1,235.68   $1,235.65   $1,235.80