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 $70.42   6.398%   $74.9255   $74.93   $74.95   $74.90  
  Purchase #2 $163.38   3.261%   $168.7078   $168.71   $168.70   $168.70  
  Purchase #3 $220.98   11.742%   $246.9275   $246.93   $246.95   $246.90  
  Purchase #4 $45.50   6.822%   $48.604   $48.60   $48.60   $48.60  
  Purchase #5 $155.61   12.189%   $174.5773   $174.58   $174.60   $174.60  
  Purchase #6 $214.77   4.353%   $224.1189   $224.12   $224.10   $224.10  
  Purchase #7 $12.38   5.129%   $13.015   $13.02   $13.00   $13.00  
  7 purchase totals = $883.04       $950.8760   $950.89   $950.90   $950.80