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 $241.81   10.524%   $267.2581   $267.26   $267.25   $267.30  
  Purchase #2 $109.85   8.638%   $119.3388   $119.34   $119.35   $119.30  
  Purchase #3 $195.97   3.284%   $202.4057   $202.41   $202.40   $202.40  
  Purchase #4 $5.47   10.405%   $6.0392   $6.04   $6.05   $6.00  
  Purchase #5 $68.67   9.589%   $75.2548   $75.25   $75.25   $75.30  
  Purchase #6 $65.50   7.716%   $70.554   $70.55   $70.55   $70.60  
  Purchase #7 $41.47   7.725%   $44.6736   $44.67   $44.65   $44.70  
  7 purchase totals = $728.74       $785.5242   $785.52   $785.50   $785.60