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 $55.68   5.414%   $58.6945   $58.69   $58.70   $58.70  
  Purchase #2 $47.31   12.649%   $53.2942   $53.29   $53.30   $53.30  
  Purchase #3 $86.43   11.352%   $96.2415   $96.24   $96.25   $96.20  
  Purchase #4 $225.49   9.199%   $246.2328   $246.23   $246.25   $246.20  
  Purchase #5 $168.58   11.210%   $187.4778   $187.48   $187.50   $187.50  
  Purchase #6 $243.68   7.824%   $262.7455   $262.75   $262.75   $262.70  
  Purchase #7 $83.60   8.579%   $90.772   $90.77   $90.75   $90.80  
  7 purchase totals = $910.77       $995.4583   $995.45   $995.50   $995.40