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 $211.41   12.433%   $237.6946   $237.69   $237.70   $237.70  
  Purchase #2 $121.72   6.344%   $129.4419   $129.44   $129.45   $129.40  
  Purchase #3 $10.50   8.193%   $11.3603   $11.36   $11.35   $11.40  
  Purchase #4 $141.65   10.463%   $156.4708   $156.47   $156.45   $156.50  
  Purchase #5 $49.63   11.421%   $55.2982   $55.30   $55.30   $55.30  
  Purchase #6 $190.61   6.710%   $203.3999   $203.40   $203.40   $203.40  
  Purchase #7 $8.78   6.710%   $9.3691   $9.37   $9.35   $9.40  
  7 purchase totals = $734.30       $803.0348   $803.03   $803.00   $803.10