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 $62.94   6.561%   $67.0695   $67.07   $67.05   $67.10  
  Purchase #2 $155.70   6.606%   $165.9855   $165.99   $166.00   $166.00  
  Purchase #3 $213.83   10.680%   $236.667   $236.67   $236.65   $236.70  
  Purchase #4 $212.42   9.669%   $232.9589   $232.96   $232.95   $233.00  
  Purchase #5 $72.30   4.793%   $75.7653   $75.77   $75.75   $75.80  
  Purchase #6 $109.81   8.220%   $118.8364   $118.84   $118.85   $118.80  
  Purchase #7 $136.39   7.549%   $146.6861   $146.69   $146.70   $146.70  
  7 purchase totals = $963.39       $1,043.9687   $1,043.99   $1,043.95   $1,044.10