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 $250.62   6.838%   $267.7574   $267.76   $267.75   $267.80  
  Purchase #2 $50.48   3.425%   $52.2089   $52.21   $52.20   $52.20  
  Purchase #3 $120.49   4.156%   $125.4976   $125.50   $125.50   $125.50  
  Purchase #4 $95.72   11.803%   $107.0178   $107.02   $107.00   $107.00  
  Purchase #5 $178.29   8.192%   $192.8955   $192.90   $192.90   $192.90  
  Purchase #6 $148.32   7.702%   $159.7436   $159.74   $159.75   $159.70  
  Purchase #7 $143.34   7.855%   $154.5994   $154.60   $154.60   $154.60  
  7 purchase totals = $987.26       $1,059.7202   $1,059.73   $1,059.70   $1,059.70