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 $60.71   9.433%   $66.4368   $66.44   $66.45   $66.40  
  Purchase #2 $103.33   5.594%   $109.1103   $109.11   $109.10   $109.10  
  Purchase #3 $197.50   3.236%   $203.8911   $203.89   $203.90   $203.90  
  Purchase #4 $69.78   3.362%   $72.126   $72.13   $72.15   $72.10  
  Purchase #5 $249.70   6.692%   $266.4099   $266.41   $266.40   $266.40  
  Purchase #6 $135.37   6.445%   $144.0946   $144.09   $144.10   $144.10  
  Purchase #7 $127.28   8.789%   $138.4666   $138.47   $138.45   $138.50  
  7 purchase totals = $943.67       $1,000.5353   $1,000.54   $1,000.55   $1,000.50