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 $235.70   9.331%   $257.6932   $257.69   $257.70   $257.70  
  Purchase #2 $15.39   11.753%   $17.1988   $17.20   $17.20   $17.20  
  Purchase #3 $200.46   5.223%   $210.93   $210.93   $210.95   $210.90  
  Purchase #4 $58.49   3.529%   $60.5541   $60.55   $60.55   $60.60  
  Purchase #5 $150.83   9.603%   $165.3142   $165.31   $165.30   $165.30  
  Purchase #6 $108.85   6.786%   $116.2366   $116.24   $116.25   $116.20  
  Purchase #7 $218.61   10.386%   $241.3148   $241.31   $241.30   $241.30  
  7 purchase totals = $988.33       $1,069.2417   $1,069.23   $1,069.25   $1,069.20