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 $85.84   8.465%   $93.1064   $93.11   $93.10   $93.10  
  Purchase #2 $227.29   3.704%   $235.7088   $235.71   $235.70   $235.70  
  Purchase #3 $176.40   3.738%   $182.9938   $182.99   $183.00   $183.00  
  Purchase #4 $218.93   11.543%   $244.2011   $244.20   $244.20   $244.20  
  Purchase #5 $138.83   7.587%   $149.363   $149.36   $149.35   $149.40  
  Purchase #6 $242.43   13.530%   $275.2308   $275.23   $275.25   $275.20  
  Purchase #7 $23.44   13.358%   $26.5711   $26.57   $26.55   $26.60  
  7 purchase totals = $1,113.16       $1,207.1750   $1,207.17   $1,207.15   $1,207.20