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 $87.28   12.253%   $97.9744   $97.97   $97.95   $98.00  
  Purchase #2 $111.39   5.385%   $117.3884   $117.39   $117.40   $117.40  
  Purchase #3 $18.80   3.190%   $19.3997   $19.40   $19.40   $19.40  
  Purchase #4 $180.91   10.411%   $199.7445   $199.74   $199.75   $199.70  
  Purchase #5 $76.74   6.319%   $81.5892   $81.59   $81.60   $81.60  
  Purchase #6 $113.83   6.777%   $121.5443   $121.54   $121.55   $121.50  
  Purchase #7 $151.72   6.359%   $161.3679   $161.37   $161.35   $161.40  
  7 purchase totals = $740.67       $799.0084   $799.00   $799.00   $799.00