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 $237.97   12.284%   $267.2022   $267.20   $267.20   $267.20  
  Purchase #2 $115.59   13.565%   $131.2698   $131.27   $131.25   $131.30  
  Purchase #3 $46.37   6.116%   $49.206   $49.21   $49.20   $49.20  
  Purchase #4 $50.29   8.724%   $54.6773   $54.68   $54.70   $54.70  
  Purchase #5 $79.43   7.830%   $85.6494   $85.65   $85.65   $85.60  
  Purchase #6 $55.84   7.370%   $59.9554   $59.96   $59.95   $60.00  
  Purchase #7 $90.58   11.778%   $101.2485   $101.25   $101.25   $101.20  
  7 purchase totals = $676.07       $749.2086   $749.22   $749.20   $749.20