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 $229.65   13.304%   $260.2026   $260.20   $260.20   $260.20  
  Purchase #2 $13.81   6.235%   $14.6711   $14.67   $14.65   $14.70  
  Purchase #3 $32.33   5.182%   $34.0053   $34.01   $34.00   $34.00  
  Purchase #4 $97.33   12.605%   $109.5984   $109.60   $109.60   $109.60  
  Purchase #5 $172.26   12.565%   $193.9045   $193.90   $193.90   $193.90  
  Purchase #6 $182.39   6.828%   $194.8436   $194.84   $194.85   $194.80  
  Purchase #7 $163.27   7.373%   $175.3079   $175.31   $175.30   $175.30  
  7 purchase totals = $891.04       $982.5334   $982.53   $982.50   $982.50