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 $42.62   4.465%   $44.523   $44.52   $44.50   $44.50  
  Purchase #2 $207.27   5.502%   $218.674   $218.67   $218.65   $218.70  
  Purchase #3 $217.73   7.790%   $234.6912   $234.69   $234.70   $234.70  
  Purchase #4 $41.76   4.182%   $43.5064   $43.51   $43.50   $43.50  
  Purchase #5 $164.48   11.629%   $183.6074   $183.61   $183.60   $183.60  
  Purchase #6 $109.92   3.342%   $113.5935   $113.59   $113.60   $113.60  
  Purchase #7 $142.70   5.336%   $150.3145   $150.31   $150.30   $150.30  
  7 purchase totals = $926.48       $988.9100   $988.90   $988.85   $988.90