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 $83.35   13.870%   $94.9106   $94.91   $94.90   $94.90  
  Purchase #2 $22.51   8.268%   $24.3711   $24.37   $24.35   $24.40  
  Purchase #3 $237.59   4.106%   $247.3454   $247.35   $247.35   $247.30  
  Purchase #4 $121.99   8.252%   $132.0566   $132.06   $132.05   $132.10  
  Purchase #5 $217.28   11.242%   $241.7066   $241.71   $241.70   $241.70  
  Purchase #6 $25.78   3.804%   $26.7607   $26.76   $26.75   $26.80  
  Purchase #7 $236.54   11.842%   $264.5511   $264.55   $264.55   $264.60  
  7 purchase totals = $945.04       $1,031.7021   $1,031.71   $1,031.65   $1,031.80