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 $89.50   7.254%   $95.9923   $95.99   $96.00   $96.00  
  Purchase #2 $221.68   12.487%   $249.3612   $249.36   $249.35   $249.40  
  Purchase #3 $113.55   13.625%   $129.0212   $129.02   $129.00   $129.00  
  Purchase #4 $159.53   5.547%   $168.3791   $168.38   $168.40   $168.40  
  Purchase #5 $66.60   13.366%   $75.5018   $75.50   $75.50   $75.50  
  Purchase #6 $201.73   11.404%   $224.7353   $224.74   $224.75   $224.70  
  Purchase #7 $83.95   4.809%   $87.9872   $87.99   $88.00   $88.00  
  7 purchase totals = $936.54       $1,030.9781   $1,030.98   $1,031.00   $1,031.00