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 $162.78   3.183%   $167.9613   $167.96   $167.95   $168.00  
  Purchase #2 $228.47   9.649%   $250.5151   $250.52   $250.50   $250.50  
  Purchase #3 $118.72   5.139%   $124.821   $124.82   $124.80   $124.80  
  Purchase #4 $221.67   7.502%   $238.2997   $238.30   $238.30   $238.30  
  Purchase #5 $110.62   5.709%   $116.9353   $116.94   $116.95   $116.90  
  Purchase #6 $85.87   8.276%   $92.9766   $92.98   $93.00   $93.00  
  Purchase #7 $76.38   12.628%   $86.0253   $86.03   $86.05   $86.00  
  7 purchase totals = $1,004.51       $1,077.5343   $1,077.55   $1,077.55   $1,077.50