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 $63.83   13.594%   $72.5071   $72.51   $72.50   $72.50  
  Purchase #2 $194.90   10.781%   $215.9122   $215.91   $215.90   $215.90  
  Purchase #3 $146.65   4.775%   $153.6525   $153.65   $153.65   $153.70  
  Purchase #4 $145.93   11.648%   $162.9279   $162.93   $162.95   $162.90  
  Purchase #5 $41.97   6.150%   $44.5512   $44.55   $44.55   $44.60  
  Purchase #6 $29.81   9.629%   $32.6804   $32.68   $32.70   $32.70  
  Purchase #7 $186.83   9.721%   $204.9917   $204.99   $205.00   $205.00  
  7 purchase totals = $809.92       $887.2230   $887.22   $887.25   $887.30