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 $50.60   10.268%   $55.7956   $55.80   $55.80   $55.80  
  Purchase #2 $125.58   9.771%   $137.8504   $137.85   $137.85   $137.90  
  Purchase #3 $105.38   3.388%   $108.9503   $108.95   $108.95   $109.00  
  Purchase #4 $61.82   5.243%   $65.0612   $65.06   $65.05   $65.10  
  Purchase #5 $250.84   12.679%   $282.644   $282.64   $282.65   $282.60  
  Purchase #6 $93.41   8.378%   $101.2359   $101.24   $101.25   $101.20  
  Purchase #7 $221.79   11.402%   $247.0785   $247.08   $247.10   $247.10  
  7 purchase totals = $909.42       $998.6159   $998.62   $998.65   $998.70