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 $51.53   8.505%   $55.9126   $55.91   $55.90   $55.90  
  Purchase #2 $75.50   4.709%   $79.0553   $79.06   $79.05   $79.10  
  Purchase #3 $169.38   9.795%   $185.9708   $185.97   $185.95   $186.00  
  Purchase #4 $187.39   9.830%   $205.8104   $205.81   $205.80   $205.80  
  Purchase #5 $57.94   4.580%   $60.5937   $60.59   $60.60   $60.60  
  Purchase #6 $210.61   11.861%   $235.5905   $235.59   $235.60   $235.60  
  Purchase #7 $176.67   12.797%   $199.2785   $199.28   $199.30   $199.30  
  7 purchase totals = $929.02       $1,022.2118   $1,022.21   $1,022.20   $1,022.30