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 $56.39   6.350%   $59.9708   $59.97   $59.95   $60.00  
  Purchase #2 $161.86   8.798%   $176.1004   $176.10   $176.10   $176.10  
  Purchase #3 $5.73   7.224%   $6.1439   $6.14   $6.15   $6.10  
  Purchase #4 $23.94   7.608%   $25.7614   $25.76   $25.75   $25.80  
  Purchase #5 $60.96   9.301%   $66.6299   $66.63   $66.65   $66.60  
  Purchase #6 $240.25   6.110%   $254.9293   $254.93   $254.95   $254.90  
  Purchase #7 $236.58   3.317%   $244.4274   $244.43   $244.45   $244.40  
  7 purchase totals = $785.71       $833.9631   $833.96   $834.00   $833.90