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 $191.75   8.437%   $207.9279   $207.93   $207.95   $207.90  
  Purchase #2 $185.87   3.249%   $191.9089   $191.91   $191.90   $191.90  
  Purchase #3 $56.95   4.563%   $59.5486   $59.55   $59.55   $59.50  
  Purchase #4 $69.51   8.102%   $75.1417   $75.14   $75.15   $75.10  
  Purchase #5 $242.57   10.234%   $267.3946   $267.39   $267.40   $267.40  
  Purchase #6 $89.96   9.321%   $98.3452   $98.35   $98.35   $98.30  
  Purchase #7 $235.64   10.412%   $260.1748   $260.17   $260.15   $260.20  
  7 purchase totals = $1,072.25       $1,160.4417   $1,160.44   $1,160.45   $1,160.30