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 $177.59   11.406%   $197.8459   $197.85   $197.85   $197.80  
  Purchase #2 $102.71   10.372%   $113.3631   $113.36   $113.35   $113.40  
  Purchase #3 $79.62   6.305%   $84.64   $84.64   $84.65   $84.60  
  Purchase #4 $189.46   7.318%   $203.3247   $203.32   $203.30   $203.30  
  Purchase #5 $107.78   13.646%   $122.4877   $122.49   $122.50   $122.50  
  Purchase #6 $247.46   13.750%   $281.4858   $281.49   $281.50   $281.50  
  Purchase #7 $18.28   5.752%   $19.3315   $19.33   $19.35   $19.30  
  7 purchase totals = $922.90       $1,022.4787   $1,022.48   $1,022.50   $1,022.40