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 $187.91   4.764%   $196.862   $196.86   $196.85   $196.90  
  Purchase #2 $92.87   4.605%   $97.1467   $97.15   $97.15   $97.10  
  Purchase #3 $36.47   10.831%   $40.4201   $40.42   $40.40   $40.40  
  Purchase #4 $235.90   12.328%   $264.9818   $264.98   $265.00   $265.00  
  Purchase #5 $177.71   11.759%   $198.6069   $198.61   $198.60   $198.60  
  Purchase #6 $81.51   3.419%   $84.2968   $84.30   $84.30   $84.30  
  Purchase #7 $142.76   13.199%   $161.6029   $161.60   $161.60   $161.60  
  7 purchase totals = $955.13       $1,043.9172   $1,043.92   $1,043.90   $1,043.90