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 $123.84   9.194%   $135.2258   $135.23   $135.25   $135.20  
  Purchase #2 $63.68   5.216%   $67.0015   $67.00   $67.00   $67.00  
  Purchase #3 $212.60   6.157%   $225.6898   $225.69   $225.70   $225.70  
  Purchase #4 $123.65   6.690%   $131.9222   $131.92   $131.90   $131.90  
  Purchase #5 $31.58   7.744%   $34.0256   $34.03   $34.05   $34.00  
  Purchase #6 $27.27   11.841%   $30.499   $30.50   $30.50   $30.50  
  Purchase #7 $72.56   5.472%   $76.5305   $76.53   $76.55   $76.50  
  7 purchase totals = $655.18       $700.8944   $700.90   $700.95   $700.80