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 $86.60   12.564%   $97.4804   $97.48   $97.50   $97.50  
  Purchase #2 $56.85   4.673%   $59.5066   $59.51   $59.50   $59.50  
  Purchase #3 $100.65   9.656%   $110.3688   $110.37   $110.35   $110.40  
  Purchase #4 $240.86   5.545%   $254.2157   $254.22   $254.20   $254.20  
  Purchase #5 $227.74   6.618%   $242.8118   $242.81   $242.80   $242.80  
  Purchase #6 $32.68   12.422%   $36.7395   $36.74   $36.75   $36.70  
  Purchase #7 $53.83   7.468%   $57.85   $57.85   $57.85   $57.90  
  7 purchase totals = $799.21       $858.9728   $858.98   $858.95   $859.00