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 $187.39   10.591%   $207.2365   $207.24   $207.25   $207.20  
  Purchase #2 $145.82   7.422%   $156.6428   $156.64   $156.65   $156.60  
  Purchase #3 $242.87   5.491%   $256.206   $256.21   $256.20   $256.20  
  Purchase #4 $198.91   5.810%   $210.4667   $210.47   $210.45   $210.50  
  Purchase #5 $66.83   8.377%   $72.4283   $72.43   $72.45   $72.40  
  Purchase #6 $149.84   8.506%   $162.5854   $162.59   $162.60   $162.60  
  Purchase #7 $133.95   6.873%   $143.1564   $143.16   $143.15   $143.20  
  7 purchase totals = $1,125.61       $1,208.7221   $1,208.74   $1,208.75   $1,208.70