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 $220.50   6.605%   $235.064   $235.06   $235.05   $235.10  
  Purchase #2 $23.50   4.873%   $24.6452   $24.65   $24.65   $24.60  
  Purchase #3 $224.34   5.609%   $236.9232   $236.92   $236.90   $236.90  
  Purchase #4 $195.44   4.158%   $203.5664   $203.57   $203.55   $203.60  
  Purchase #5 $118.68   5.266%   $124.9297   $124.93   $124.95   $124.90  
  Purchase #6 $242.71   4.725%   $254.178   $254.18   $254.20   $254.20  
  Purchase #7 $207.81   9.267%   $227.0678   $227.07   $227.05   $227.10  
  7 purchase totals = $1,232.98       $1,306.3743   $1,306.38   $1,306.35   $1,306.40