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 $218.95   10.354%   $241.6201   $241.62   $241.60   $241.60  
  Purchase #2 $222.69   6.370%   $236.8754   $236.88   $236.90   $236.90  
  Purchase #3 $188.66   9.259%   $206.128   $206.13   $206.15   $206.10  
  Purchase #4 $247.90   11.161%   $275.5681   $275.57   $275.55   $275.60  
  Purchase #5 $59.93   11.713%   $66.9496   $66.95   $66.95   $66.90  
  Purchase #6 $5.48   3.735%   $5.6847   $5.68   $5.70   $5.70  
  Purchase #7 $27.37   9.136%   $29.8705   $29.87   $29.85   $29.90  
  7 purchase totals = $970.98       $1,062.6964   $1,062.70   $1,062.70   $1,062.70