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 $69.29   4.343%   $72.2993   $72.30   $72.30   $72.30  
  Purchase #2 $123.27   9.759%   $135.2999   $135.30   $135.30   $135.30  
  Purchase #3 $199.42   11.660%   $222.6724   $222.67   $222.65   $222.70  
  Purchase #4 $80.93   7.191%   $86.7497   $86.75   $86.75   $86.70  
  Purchase #5 $109.70   5.110%   $115.3057   $115.31   $115.30   $115.30  
  Purchase #6 $237.83   9.333%   $260.0267   $260.03   $260.05   $260.00  
  Purchase #7 $27.54   9.530%   $30.1646   $30.16   $30.15   $30.20  
  7 purchase totals = $847.98       $922.5183   $922.52   $922.50   $922.50