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 $82.61   10.320%   $91.1354   $91.14   $91.15   $91.10  
  Purchase #2 $174.98   4.555%   $182.9503   $182.95   $182.95   $183.00  
  Purchase #3 $94.60   8.308%   $102.4594   $102.46   $102.45   $102.50  
  Purchase #4 $156.39   7.188%   $167.6313   $167.63   $167.65   $167.60  
  Purchase #5 $133.65   6.306%   $142.078   $142.08   $142.10   $142.10  
  Purchase #6 $128.82   5.632%   $136.0751   $136.08   $136.10   $136.10  
  Purchase #7 $178.71   3.147%   $184.334   $184.33   $184.35   $184.30  
  7 purchase totals = $949.76       $1,006.6635   $1,006.67   $1,006.75   $1,006.70