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 $65.50   9.277%   $71.5764   $71.58   $71.60   $71.60  
  Purchase #2 $221.55   10.412%   $244.6178   $244.62   $244.60   $244.60  
  Purchase #3 $239.62   13.468%   $271.892   $271.89   $271.90   $271.90  
  Purchase #4 $215.61   11.815%   $241.0843   $241.08   $241.10   $241.10  
  Purchase #5 $84.38   12.504%   $94.9309   $94.93   $94.95   $94.90  
  Purchase #6 $245.81   5.419%   $259.1304   $259.13   $259.15   $259.10  
  Purchase #7 $18.44   3.224%   $19.0345   $19.03   $19.05   $19.00  
  7 purchase totals = $1,090.91       $1,202.2663   $1,202.26   $1,202.35   $1,202.20