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 $208.50   10.756%   $230.9263   $230.93   $230.95   $230.90  
  Purchase #2 $171.72   13.235%   $194.4471   $194.45   $194.45   $194.40  
  Purchase #3 $233.78   5.530%   $246.708   $246.71   $246.70   $246.70  
  Purchase #4 $55.98   11.186%   $62.2419   $62.24   $62.25   $62.20  
  Purchase #5 $7.46   13.115%   $8.4384   $8.44   $8.45   $8.40  
  Purchase #6 $11.48   13.745%   $13.0579   $13.06   $13.05   $13.10  
  Purchase #7 $165.67   8.245%   $179.3295   $179.33   $179.35   $179.30  
  7 purchase totals = $854.59       $935.1491   $935.16   $935.20   $935.00