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 $68.74   11.743%   $76.8121   $76.81   $76.80   $76.80  
  Purchase #2 $68.85   11.686%   $76.8958   $76.90   $76.90   $76.90  
  Purchase #3 $189.92   4.291%   $198.0695   $198.07   $198.05   $198.10  
  Purchase #4 $195.80   7.813%   $211.0979   $211.10   $211.10   $211.10  
  Purchase #5 $171.41   9.502%   $187.6974   $187.70   $187.70   $187.70  
  Purchase #6 $223.74   13.517%   $253.9829   $253.98   $254.00   $254.00  
  Purchase #7 $224.85   11.606%   $250.9461   $250.95   $250.95   $250.90  
  7 purchase totals = $1,143.31       $1,255.5017   $1,255.51   $1,255.50   $1,255.50