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 $250.72   13.703%   $285.0762   $285.08   $285.10   $285.10  
  Purchase #2 $33.58   5.235%   $35.3379   $35.34   $35.35   $35.30  
  Purchase #3 $220.94   5.758%   $233.6617   $233.66   $233.65   $233.70  
  Purchase #4 $200.57   10.274%   $221.1766   $221.18   $221.20   $221.20  
  Purchase #5 $90.93   8.791%   $98.9237   $98.92   $98.90   $98.90  
  Purchase #6 $224.27   6.270%   $238.3317   $238.33   $238.35   $238.30  
  Purchase #7 $229.68   5.338%   $241.9403   $241.94   $241.95   $241.90  
  7 purchase totals = $1,250.69       $1,354.4481   $1,354.45   $1,354.50   $1,354.40