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 $190.54   10.134%   $209.8493   $209.85   $209.85   $209.80  
  Purchase #2 $50.38   9.659%   $55.2462   $55.25   $55.25   $55.20  
  Purchase #3 $155.62   3.394%   $160.9017   $160.90   $160.90   $160.90  
  Purchase #4 $74.79   3.714%   $77.5677   $77.57   $77.55   $77.60  
  Purchase #5 $77.31   11.241%   $86.0004   $86.00   $86.00   $86.00  
  Purchase #6 $244.82   9.737%   $268.6581   $268.66   $268.65   $268.70  
  Purchase #7 $133.53   11.496%   $148.8806   $148.88   $148.90   $148.90  
  7 purchase totals = $926.99       $1,007.1040   $1,007.11   $1,007.10   $1,007.10