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 $67.40   3.643%   $69.8554   $69.86   $69.85   $69.90  
  Purchase #2 $91.29   6.264%   $97.0084   $97.01   $97.00   $97.00  
  Purchase #3 $115.36   3.269%   $119.1311   $119.13   $119.15   $119.10  
  Purchase #4 $59.29   3.458%   $61.3402   $61.34   $61.35   $61.30  
  Purchase #5 $69.73   8.756%   $75.8356   $75.84   $75.85   $75.80  
  Purchase #6 $230.97   9.335%   $252.531   $252.53   $252.55   $252.50  
  Purchase #7 $107.41   12.711%   $121.0629   $121.06   $121.05   $121.10  
  7 purchase totals = $741.45       $796.7646   $796.77   $796.80   $796.70