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 $244.36   13.326%   $276.9234   $276.92   $276.90   $276.90  
  Purchase #2 $102.52   12.694%   $115.5339   $115.53   $115.55   $115.50  
  Purchase #3 $226.87   6.337%   $241.2468   $241.25   $241.25   $241.20  
  Purchase #4 $157.91   6.574%   $168.291   $168.29   $168.30   $168.30  
  Purchase #5 $165.32   10.584%   $182.8175   $182.82   $182.80   $182.80  
  Purchase #6 $234.78   11.121%   $260.8899   $260.89   $260.90   $260.90  
  Purchase #7 $51.89   8.760%   $56.4356   $56.44   $56.45   $56.40  
  7 purchase totals = $1,183.65       $1,302.1381   $1,302.14   $1,302.15   $1,302.00