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 $208.38   7.658%   $224.3377   $224.34   $224.35   $224.30  
  Purchase #2 $121.40   4.612%   $126.999   $127.00   $127.00   $127.00  
  Purchase #3 $10.49   3.625%   $10.8703   $10.87   $10.85   $10.90  
  Purchase #4 $226.64   5.799%   $239.7829   $239.78   $239.80   $239.80  
  Purchase #5 $169.96   13.813%   $193.4366   $193.44   $193.45   $193.40  
  Purchase #6 $41.26   13.558%   $46.854   $46.85   $46.85   $46.90  
  Purchase #7 $70.69   5.585%   $74.638   $74.64   $74.65   $74.60  
  7 purchase totals = $848.82       $916.9185   $916.92   $916.95   $916.90