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 $63.49   11.356%   $70.6999   $70.70   $70.70   $70.70  
  Purchase #2 $234.71   9.468%   $256.9323   $256.93   $256.95   $256.90  
  Purchase #3 $149.80   3.386%   $154.8722   $154.87   $154.85   $154.90  
  Purchase #4 $63.72   4.170%   $66.3771   $66.38   $66.40   $66.40  
  Purchase #5 $179.67   6.213%   $190.8329   $190.83   $190.85   $190.80  
  Purchase #6 $187.55   6.395%   $199.5438   $199.54   $199.55   $199.50  
  Purchase #7 $217.62   12.665%   $245.1816   $245.18   $245.20   $245.20  
  7 purchase totals = $1,096.56       $1,184.4398   $1,184.43   $1,184.50   $1,184.40