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 $246.81   8.691%   $268.2603   $268.26   $268.25   $268.30  
  Purchase #2 $28.26   10.702%   $31.2844   $31.28   $31.30   $31.30  
  Purchase #3 $93.66   6.347%   $99.6046   $99.60   $99.60   $99.60  
  Purchase #4 $181.50   6.571%   $193.4264   $193.43   $193.45   $193.40  
  Purchase #5 $100.59   13.139%   $113.8065   $113.81   $113.80   $113.80  
  Purchase #6 $150.53   9.316%   $164.5534   $164.55   $164.55   $164.60  
  Purchase #7 $204.32   9.649%   $224.0348   $224.03   $224.05   $224.00  
  7 purchase totals = $1,005.67       $1,094.9704   $1,094.96   $1,095.00   $1,095.00