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 $43.40   10.412%   $47.9188   $47.92   $47.90   $47.90  
  Purchase #2 $150.96   7.139%   $161.737   $161.74   $161.75   $161.70  
  Purchase #3 $216.25   4.795%   $226.6192   $226.62   $226.60   $226.60  
  Purchase #4 $74.86   13.592%   $85.035   $85.04   $85.05   $85.00  
  Purchase #5 $175.91   3.462%   $182   $182.00   $182.00   $182.00  
  Purchase #6 $53.95   13.562%   $61.2667   $61.27   $61.25   $61.30  
  Purchase #7 $179.29   3.783%   $186.0725   $186.07   $186.05   $186.10  
  7 purchase totals = $894.62       $950.6492   $950.66   $950.60   $950.60