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 $75.57   9.866%   $83.0257   $83.03   $83.05   $83.00  
  Purchase #2 $228.88   7.721%   $246.5518   $246.55   $246.55   $246.60  
  Purchase #3 $146.27   7.465%   $157.1891   $157.19   $157.20   $157.20  
  Purchase #4 $171.76   7.673%   $184.9391   $184.94   $184.95   $184.90  
  Purchase #5 $46.48   8.679%   $50.514   $50.51   $50.50   $50.50  
  Purchase #6 $38.48   5.804%   $40.7134   $40.71   $40.70   $40.70  
  Purchase #7 $151.70   7.350%   $162.85   $162.85   $162.85   $162.90  
  7 purchase totals = $859.14       $925.7831   $925.78   $925.80   $925.80