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 $44.65   4.148%   $46.5021   $46.50   $46.50   $46.50  
  Purchase #2 $183.54   8.532%   $199.1996   $199.20   $199.20   $199.20  
  Purchase #3 $50.64   10.446%   $55.9299   $55.93   $55.95   $55.90  
  Purchase #4 $137.38   3.818%   $142.6252   $142.63   $142.65   $142.60  
  Purchase #5 $100.52   12.628%   $113.2137   $113.21   $113.20   $113.20  
  Purchase #6 $124.94   3.421%   $129.2142   $129.21   $129.20   $129.20  
  Purchase #7 $119.51   7.699%   $128.7111   $128.71   $128.70   $128.70  
  7 purchase totals = $761.18       $815.3958   $815.39   $815.40   $815.30