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 $54.64   13.792%   $62.1759   $62.18   $62.20   $62.20  
  Purchase #2 $98.35   11.750%   $109.9061   $109.91   $109.90   $109.90  
  Purchase #3 $133.63   8.785%   $145.3694   $145.37   $145.35   $145.40  
  Purchase #4 $70.92   8.640%   $77.0475   $77.05   $77.05   $77.00  
  Purchase #5 $226.72   8.706%   $246.4582   $246.46   $246.45   $246.50  
  Purchase #6 $143.85   5.457%   $151.6999   $151.70   $151.70   $151.70  
  Purchase #7 $248.63   7.146%   $266.3971   $266.40   $266.40   $266.40  
  7 purchase totals = $976.74       $1,059.0541   $1,059.07   $1,059.05   $1,059.10