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 $72.63   3.315%   $75.0377   $75.04   $75.05   $75.00  
  Purchase #2 $62.73   7.366%   $67.3507   $67.35   $67.35   $67.40  
  Purchase #3 $72.77   10.438%   $80.3657   $80.37   $80.35   $80.40  
  Purchase #4 $44.90   6.736%   $47.9245   $47.92   $47.90   $47.90  
  Purchase #5 $68.70   12.417%   $77.2305   $77.23   $77.25   $77.20  
  Purchase #6 $177.70   11.850%   $198.7575   $198.76   $198.75   $198.80  
  Purchase #7 $148.29   12.807%   $167.2815   $167.28   $167.30   $167.30  
  7 purchase totals = $647.72       $713.9481   $713.95   $713.95   $714.00