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 $244.47   12.115%   $274.0875   $274.09   $274.10   $274.10  
  Purchase #2 $111.96   4.769%   $117.2994   $117.30   $117.30   $117.30  
  Purchase #3 $75.69   4.231%   $78.8924   $78.89   $78.90   $78.90  
  Purchase #4 $43.85   11.624%   $48.9471   $48.95   $48.95   $48.90  
  Purchase #5 $135.40   6.361%   $144.0128   $144.01   $144.00   $144.00  
  Purchase #6 $221.58   11.333%   $246.6917   $246.69   $246.70   $246.70  
  Purchase #7 $21.69   9.351%   $23.7182   $23.72   $23.70   $23.70  
  7 purchase totals = $854.64       $933.6491   $933.65   $933.65   $933.60