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 $14.94   10.579%   $16.5205   $16.52   $16.50   $16.50  
  Purchase #2 $135.61   5.585%   $143.1838   $143.18   $143.20   $143.20  
  Purchase #3 $156.63   10.787%   $173.5257   $173.53   $173.55   $173.50  
  Purchase #4 $172.40   6.626%   $183.8232   $183.82   $183.80   $183.80  
  Purchase #5 $182.27   10.608%   $201.6052   $201.61   $201.60   $201.60  
  Purchase #6 $200.36   4.148%   $208.6709   $208.67   $208.65   $208.70  
  Purchase #7 $99.50   4.465%   $103.9427   $103.94   $103.95   $103.90  
  7 purchase totals = $961.71       $1,031.2720   $1,031.27   $1,031.25   $1,031.20