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 $67.61   12.176%   $75.8422   $75.84   $75.85   $75.80  
  Purchase #2 $94.86   6.695%   $101.2109   $101.21   $101.20   $101.20  
  Purchase #3 $109.44   12.799%   $123.4472   $123.45   $123.45   $123.40  
  Purchase #4 $67.32   8.464%   $73.018   $73.02   $73.00   $73.00  
  Purchase #5 $245.85   11.476%   $274.0637   $274.06   $274.05   $274.10  
  Purchase #6 $151.88   10.807%   $168.2937   $168.29   $168.30   $168.30  
  Purchase #7 $60.66   11.631%   $67.7154   $67.72   $67.70   $67.70  
  7 purchase totals = $797.62       $883.5911   $883.59   $883.55   $883.50