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 $30.96   12.467%   $34.8198   $34.82   $34.80   $34.80  
  Purchase #2 $23.99   9.652%   $26.3055   $26.31   $26.30   $26.30  
  Purchase #3 $234.89   6.874%   $251.0363   $251.04   $251.05   $251.00  
  Purchase #4 $38.88   3.455%   $40.2233   $40.22   $40.20   $40.20  
  Purchase #5 $64.70   8.485%   $70.1898   $70.19   $70.20   $70.20  
  Purchase #6 $89.97   4.755%   $94.2481   $94.25   $94.25   $94.20  
  Purchase #7 $223.47   11.744%   $249.7143   $249.71   $249.70   $249.70  
  7 purchase totals = $706.86       $766.5371   $766.54   $766.50   $766.40