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 $239.45   11.760%   $267.6093   $267.61   $267.60   $267.60  
  Purchase #2 $241.31   12.457%   $271.37   $271.37   $271.35   $271.40  
  Purchase #3 $145.40   12.221%   $163.1693   $163.17   $163.15   $163.20  
  Purchase #4 $155.67   3.620%   $161.3053   $161.31   $161.30   $161.30  
  Purchase #5 $44.75   13.117%   $50.6199   $50.62   $50.60   $50.60  
  Purchase #6 $181.60   4.558%   $189.8773   $189.88   $189.90   $189.90  
  Purchase #7 $142.63   11.601%   $159.1765   $159.18   $159.20   $159.20  
  7 purchase totals = $1,150.81       $1,263.1276   $1,263.14   $1,263.10   $1,263.20