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 $208.64   10.542%   $230.6348   $230.63   $230.65   $230.60  
  Purchase #2 $27.91   5.189%   $29.3582   $29.36   $29.35   $29.40  
  Purchase #3 $91.34   3.753%   $94.768   $94.77   $94.75   $94.80  
  Purchase #4 $212.33   5.825%   $224.6982   $224.70   $224.70   $224.70  
  Purchase #5 $177.78   6.584%   $189.485   $189.49   $189.50   $189.50  
  Purchase #6 $135.68   9.646%   $148.7677   $148.77   $148.75   $148.80  
  Purchase #7 $132.38   10.241%   $145.937   $145.94   $145.95   $145.90  
  7 purchase totals = $986.06       $1,063.6489   $1,063.66   $1,063.65   $1,063.70