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 $6.86   13.525%   $7.7878   $7.79   $7.80   $7.80  
  Purchase #2 $213.68   5.479%   $225.3875   $225.39   $225.40   $225.40  
  Purchase #3 $37.92   7.695%   $40.8379   $40.84   $40.85   $40.80  
  Purchase #4 $187.52   4.509%   $195.9753   $195.98   $196.00   $196.00  
  Purchase #5 $121.77   8.496%   $132.1156   $132.12   $132.10   $132.10  
  Purchase #6 $172.66   6.418%   $183.7413   $183.74   $183.75   $183.70  
  Purchase #7 $104.96   11.392%   $116.917   $116.92   $116.90   $116.90  
  7 purchase totals = $845.37       $902.7624   $902.78   $902.80   $902.70