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 $24.82   6.564%   $26.4492   $26.45   $26.45   $26.40  
  Purchase #2 $246.46   5.479%   $259.9635   $259.96   $259.95   $260.00  
  Purchase #3 $35.48   6.202%   $37.6805   $37.68   $37.70   $37.70  
  Purchase #4 $88.64   11.334%   $98.6865   $98.69   $98.70   $98.70  
  Purchase #5 $190.51   8.408%   $206.5281   $206.53   $206.55   $206.50  
  Purchase #6 $202.65   10.446%   $223.8188   $223.82   $223.80   $223.80  
  Purchase #7 $124.46   7.224%   $133.451   $133.45   $133.45   $133.50  
  7 purchase totals = $913.02       $986.5776   $986.58   $986.60   $986.60