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 $39.86   4.532%   $41.6665   $41.67   $41.65   $41.70  
  Purchase #2 $199.70   12.452%   $224.5666   $224.57   $224.55   $224.60  
  Purchase #3 $226.92   8.589%   $246.4102   $246.41   $246.40   $246.40  
  Purchase #4 $72.87   8.416%   $79.0027   $79.00   $79.00   $79.00  
  Purchase #5 $101.79   6.815%   $108.727   $108.73   $108.75   $108.70  
  Purchase #6 $157.91   13.715%   $179.5674   $179.57   $179.55   $179.60  
  Purchase #7 $192.87   5.807%   $204.07   $204.07   $204.05   $204.10  
  7 purchase totals = $991.92       $1,084.0104   $1,084.02   $1,083.95   $1,084.10