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 $58.86   11.792%   $65.8008   $65.80   $65.80   $65.80  
  Purchase #2 $61.68   9.433%   $67.4983   $67.50   $67.50   $67.50  
  Purchase #3 $178.71   11.705%   $199.628   $199.63   $199.65   $199.60  
  Purchase #4 $245.97   5.632%   $259.823   $259.82   $259.80   $259.80  
  Purchase #5 $145.92   10.698%   $161.5305   $161.53   $161.55   $161.50  
  Purchase #6 $203.28   7.456%   $218.4366   $218.44   $218.45   $218.40  
  Purchase #7 $26.29   7.609%   $28.2904   $28.29   $28.30   $28.30  
  7 purchase totals = $920.71       $1,001.0076   $1,001.01   $1,001.05   $1,000.90