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 $83.62   12.216%   $93.835   $93.84   $93.85   $93.80  
  Purchase #2 $66.32   11.357%   $73.852   $73.85   $73.85   $73.90  
  Purchase #3 $224.63   8.489%   $243.6988   $243.70   $243.70   $243.70  
  Purchase #4 $145.91   9.156%   $159.2695   $159.27   $159.25   $159.30  
  Purchase #5 $71.54   3.206%   $73.8336   $73.83   $73.85   $73.80  
  Purchase #6 $11.62   6.575%   $12.384   $12.38   $12.40   $12.40  
  Purchase #7 $158.37   9.366%   $173.2029   $173.20   $173.20   $173.20  
  7 purchase totals = $762.01       $830.0758   $830.07   $830.10   $830.10