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 $154.75   10.261%   $170.6289   $170.63   $170.65   $170.60  
  Purchase #2 $44.86   4.455%   $46.8585   $46.86   $46.85   $46.90  
  Purchase #3 $95.44   8.106%   $103.1764   $103.18   $103.20   $103.20  
  Purchase #4 $250.72   7.771%   $270.2035   $270.20   $270.20   $270.20  
  Purchase #5 $63.62   7.858%   $68.6193   $68.62   $68.60   $68.60  
  Purchase #6 $118.27   12.577%   $133.1448   $133.14   $133.15   $133.10  
  Purchase #7 $111.56   6.574%   $118.894   $118.89   $118.90   $118.90  
  7 purchase totals = $839.22       $911.5254   $911.52   $911.55   $911.50