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 $13.76   6.593%   $14.6672   $14.67   $14.65   $14.70  
  Purchase #2 $237.38   4.329%   $247.6562   $247.66   $247.65   $247.70  
  Purchase #3 $52.33   12.424%   $58.8315   $58.83   $58.85   $58.80  
  Purchase #4 $191.27   13.489%   $217.0704   $217.07   $217.05   $217.10  
  Purchase #5 $177.95   8.142%   $192.4387   $192.44   $192.45   $192.40  
  Purchase #6 $224.75   12.463%   $252.7606   $252.76   $252.75   $252.80  
  Purchase #7 $233.82   9.336%   $255.6494   $255.65   $255.65   $255.60  
  7 purchase totals = $1,131.26       $1,239.0740   $1,239.08   $1,239.05   $1,239.10