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 $55.44   5.733%   $58.6184   $58.62   $58.60   $58.60  
  Purchase #2 $157.55   11.211%   $175.2129   $175.21   $175.20   $175.20  
  Purchase #3 $108.29   9.609%   $118.6956   $118.70   $118.70   $118.70  
  Purchase #4 $195.38   8.580%   $212.1436   $212.14   $212.15   $212.10  
  Purchase #5 $172.65   10.575%   $190.9077   $190.91   $190.90   $190.90  
  Purchase #6 $177.52   7.738%   $191.2565   $191.26   $191.25   $191.30  
  Purchase #7 $80.58   10.378%   $88.9426   $88.94   $88.95   $88.90  
  7 purchase totals = $947.41       $1,035.7773   $1,035.78   $1,035.75   $1,035.70