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 $183.91   10.137%   $202.553   $202.55   $202.55   $202.60  
  Purchase #2 $63.30   11.143%   $70.3535   $70.35   $70.35   $70.40  
  Purchase #3 $69.76   4.397%   $72.8273   $72.83   $72.85   $72.80  
  Purchase #4 $22.44   6.128%   $23.8151   $23.82   $23.80   $23.80  
  Purchase #5 $14.80   11.831%   $16.551   $16.55   $16.55   $16.60  
  Purchase #6 $210.97   10.495%   $233.1113   $233.11   $233.10   $233.10  
  Purchase #7 $61.67   7.556%   $66.3298   $66.33   $66.35   $66.30  
  7 purchase totals = $626.85       $685.5410   $685.54   $685.55   $685.60