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 $228.46   7.246%   $245.0142   $245.01   $245.00   $245.00  
  Purchase #2 $40.59   7.354%   $43.575   $43.58   $43.60   $43.60  
  Purchase #3 $170.37   5.367%   $179.5138   $179.51   $179.50   $179.50  
  Purchase #4 $22.63   12.209%   $25.3929   $25.39   $25.40   $25.40  
  Purchase #5 $148.76   11.614%   $166.037   $166.04   $166.05   $166.00  
  Purchase #6 $132.48   6.173%   $140.658   $140.66   $140.65   $140.70  
  Purchase #7 $103.84   11.747%   $116.0381   $116.04   $116.05   $116.00  
  7 purchase totals = $847.13       $916.2290   $916.23   $916.25   $916.20