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 $143.32   3.677%   $148.5899   $148.59   $148.60   $148.60  
  Purchase #2 $79.33   6.673%   $84.6237   $84.62   $84.60   $84.60  
  Purchase #3 $140.40   12.171%   $157.4881   $157.49   $157.50   $157.50  
  Purchase #4 $75.29   3.233%   $77.7241   $77.72   $77.70   $77.70  
  Purchase #5 $97.61   3.510%   $101.0361   $101.04   $101.05   $101.00  
  Purchase #6 $241.57   11.497%   $269.3433   $269.34   $269.35   $269.30  
  Purchase #7 $209.52   12.196%   $235.0731   $235.07   $235.05   $235.10  
  7 purchase totals = $987.04       $1,073.8783   $1,073.87   $1,073.85   $1,073.80