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 $118.48   11.637%   $132.2675   $132.27   $132.25   $132.30  
  Purchase #2 $160.99   13.287%   $182.3807   $182.38   $182.40   $182.40  
  Purchase #3 $236.50   11.839%   $264.4992   $264.50   $264.50   $264.50  
  Purchase #4 $244.48   12.761%   $275.6781   $275.68   $275.70   $275.70  
  Purchase #5 $168.43   3.566%   $174.4362   $174.44   $174.45   $174.40  
  Purchase #6 $150.46   8.609%   $163.4131   $163.41   $163.40   $163.40  
  Purchase #7 $25.65   4.617%   $26.8343   $26.83   $26.85   $26.80  
  7 purchase totals = $1,104.99       $1,219.5091   $1,219.51   $1,219.55   $1,219.50