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 $64.97   10.861%   $72.0264   $72.03   $72.05   $72.00  
  Purchase #2 $32.73   7.558%   $35.2037   $35.20   $35.20   $35.20  
  Purchase #3 $218.52   8.226%   $236.4955   $236.50   $236.50   $236.50  
  Purchase #4 $153.44   8.831%   $166.9903   $166.99   $167.00   $167.00  
  Purchase #5 $239.93   9.518%   $262.7665   $262.77   $262.75   $262.80  
  Purchase #6 $72.74   11.528%   $81.1255   $81.13   $81.15   $81.10  
  Purchase #7 $205.27   13.796%   $233.589   $233.59   $233.60   $233.60  
  7 purchase totals = $987.60       $1,088.1969   $1,088.21   $1,088.25   $1,088.20