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 $25.96   3.667%   $26.912   $26.91   $26.90   $26.90  
  Purchase #2 $82.43   3.228%   $85.0908   $85.09   $85.10   $85.10  
  Purchase #3 $232.27   10.411%   $256.4516   $256.45   $256.45   $256.50  
  Purchase #4 $250.57   8.873%   $272.8031   $272.80   $272.80   $272.80  
  Purchase #5 $226.34   13.827%   $257.636   $257.64   $257.65   $257.60  
  Purchase #6 $34.88   6.154%   $37.0265   $37.03   $37.05   $37.00  
  Purchase #7 $112.51   7.304%   $120.7277   $120.73   $120.75   $120.70  
  7 purchase totals = $964.96       $1,056.6477   $1,056.65   $1,056.70   $1,056.60