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 $60.62   9.715%   $66.5092   $66.51   $66.50   $66.50  
  Purchase #2 $216.65   10.230%   $238.8133   $238.81   $238.80   $238.80  
  Purchase #3 $67.61   9.349%   $73.9309   $73.93   $73.95   $73.90  
  Purchase #4 $221.86   9.173%   $242.2112   $242.21   $242.20   $242.20  
  Purchase #5 $148.28   13.713%   $168.6136   $168.61   $168.60   $168.60  
  Purchase #6 $188.35   12.465%   $211.8278   $211.83   $211.85   $211.80  
  Purchase #7 $234.65   5.408%   $247.3399   $247.34   $247.35   $247.30  
  7 purchase totals = $1,138.02       $1,249.2459   $1,249.24   $1,249.25   $1,249.10