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 $105.47   10.341%   $116.3767   $116.38   $116.40   $116.40  
  Purchase #2 $91.72   13.274%   $103.8949   $103.89   $103.90   $103.90  
  Purchase #3 $234.80   7.309%   $251.9615   $251.96   $251.95   $252.00  
  Purchase #4 $219.81   8.500%   $238.4939   $238.49   $238.50   $238.50  
  Purchase #5 $97.86   12.330%   $109.9261   $109.93   $109.95   $109.90  
  Purchase #6 $13.95   7.727%   $15.0279   $15.03   $15.05   $15.00  
  Purchase #7 $13.75   3.770%   $14.2684   $14.27   $14.25   $14.30  
  7 purchase totals = $777.36       $849.9494   $849.95   $850.00   $850.00