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 $44.66   10.449%   $49.3265   $49.33   $49.35   $49.30  
  Purchase #2 $178.51   9.628%   $195.6969   $195.70   $195.70   $195.70  
  Purchase #3 $32.94   3.847%   $34.2072   $34.21   $34.20   $34.20  
  Purchase #4 $188.44   13.822%   $214.4862   $214.49   $214.50   $214.50  
  Purchase #5 $60.90   6.471%   $64.8408   $64.84   $64.85   $64.80  
  Purchase #6 $64.81   4.869%   $67.9656   $67.97   $67.95   $68.00  
  Purchase #7 $245.63   13.855%   $279.662   $279.66   $279.65   $279.70  
  7 purchase totals = $815.89       $906.1852   $906.20   $906.20   $906.20