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 $22.92   5.842%   $24.259   $24.26   $24.25   $24.30  
  Purchase #2 $75.39   8.518%   $81.8117   $81.81   $81.80   $81.80  
  Purchase #3 $168.40   3.412%   $174.1458   $174.15   $174.15   $174.10  
  Purchase #4 $116.64   8.624%   $126.699   $126.70   $126.70   $126.70  
  Purchase #5 $231.54   13.673%   $263.1985   $263.20   $263.20   $263.20  
  Purchase #6 $31.54   4.619%   $32.9968   $33.00   $33.00   $33.00  
  Purchase #7 $71.55   10.599%   $79.1336   $79.13   $79.15   $79.10  
  7 purchase totals = $717.98       $782.2444   $782.25   $782.25   $782.20