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 $55.56   12.137%   $62.3033   $62.30   $62.30   $62.30  
  Purchase #2 $101.85   11.451%   $113.5128   $113.51   $113.50   $113.50  
  Purchase #3 $110.48   6.137%   $117.2602   $117.26   $117.25   $117.30  
  Purchase #4 $136.87   11.422%   $152.5033   $152.50   $152.50   $152.50  
  Purchase #5 $126.75   7.649%   $136.4451   $136.45   $136.45   $136.40  
  Purchase #6 $155.27   5.511%   $163.8269   $163.83   $163.85   $163.80  
  Purchase #7 $89.32   9.475%   $97.7831   $97.78   $97.80   $97.80  
  7 purchase totals = $776.10       $843.6347   $843.63   $843.65   $843.60