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 $85.95   6.511%   $91.5462   $91.55   $91.55   $91.50  
  Purchase #2 $179.80   7.498%   $193.2814   $193.28   $193.30   $193.30  
  Purchase #3 $208.54   13.331%   $236.3405   $236.34   $236.35   $236.30  
  Purchase #4 $70.62   3.155%   $72.8481   $72.85   $72.85   $72.80  
  Purchase #5 $68.88   10.659%   $76.2219   $76.22   $76.20   $76.20  
  Purchase #6 $153.68   9.274%   $167.9323   $167.93   $167.95   $167.90  
  Purchase #7 $102.46   9.489%   $112.1824   $112.18   $112.20   $112.20  
  7 purchase totals = $869.93       $950.3528   $950.35   $950.40   $950.20