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 $180.95   6.867%   $193.3758   $193.38   $193.40   $193.40  
  Purchase #2 $220.83   12.153%   $247.6675   $247.67   $247.65   $247.70  
  Purchase #3 $69.71   3.474%   $72.1317   $72.13   $72.15   $72.10  
  Purchase #4 $182.92   4.800%   $191.7002   $191.70   $191.70   $191.70  
  Purchase #5 $219.37   7.446%   $235.7043   $235.70   $235.70   $235.70  
  Purchase #6 $244.63   5.716%   $258.6131   $258.61   $258.60   $258.60  
  Purchase #7 $210.50   12.352%   $236.501   $236.50   $236.50   $236.50  
  7 purchase totals = $1,328.91       $1,435.6936   $1,435.69   $1,435.70   $1,435.70