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 $127.94   6.509%   $136.2676   $136.27   $136.25   $136.30  
  Purchase #2 $180.46   4.495%   $188.5717   $188.57   $188.55   $188.60  
  Purchase #3 $147.34   13.175%   $166.752   $166.75   $166.75   $166.80  
  Purchase #4 $140.93   5.260%   $148.3429   $148.34   $148.35   $148.30  
  Purchase #5 $176.30   7.498%   $189.519   $189.52   $189.50   $189.50  
  Purchase #6 $117.91   7.319%   $126.5398   $126.54   $126.55   $126.50  
  Purchase #7 $183.60   5.644%   $193.9624   $193.96   $193.95   $194.00  
  7 purchase totals = $1,074.48       $1,149.9554   $1,149.95   $1,149.90   $1,150.00