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 $104.98   6.417%   $111.7166   $111.72   $111.70   $111.70  
  Purchase #2 $85.58   8.717%   $93.04   $93.04   $93.05   $93.00  
  Purchase #3 $21.40   5.427%   $22.5614   $22.56   $22.55   $22.60  
  Purchase #4 $179.47   6.830%   $191.7278   $191.73   $191.75   $191.70  
  Purchase #5 $239.66   4.473%   $250.38   $250.38   $250.40   $250.40  
  Purchase #6 $205.87   11.702%   $229.9609   $229.96   $229.95   $230.00  
  Purchase #7 $50.30   10.585%   $55.6243   $55.62   $55.60   $55.60  
  7 purchase totals = $887.26       $955.0110   $955.01   $955.00   $955.00