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 $244.53   7.137%   $261.9821   $261.98   $262.00   $262.00  
  Purchase #2 $42.44   6.666%   $45.2691   $45.27   $45.25   $45.30  
  Purchase #3 $15.48   5.291%   $16.299   $16.30   $16.30   $16.30  
  Purchase #4 $205.53   7.285%   $220.5029   $220.50   $220.50   $220.50  
  Purchase #5 $71.62   12.556%   $80.6126   $80.61   $80.60   $80.60  
  Purchase #6 $228.54   3.263%   $235.9973   $236.00   $236.00   $236.00  
  Purchase #7 $122.61   11.805%   $137.0841   $137.08   $137.10   $137.10  
  7 purchase totals = $930.75       $997.7471   $997.74   $997.75   $997.80