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 $85.83   12.541%   $96.5939   $96.59   $96.60   $96.60  
  Purchase #2 $110.74   4.491%   $115.7133   $115.71   $115.70   $115.70  
  Purchase #3 $131.98   4.739%   $138.2345   $138.23   $138.25   $138.20  
  Purchase #4 $125.82   11.660%   $140.4906   $140.49   $140.50   $140.50  
  Purchase #5 $230.92   4.586%   $241.51   $241.51   $241.50   $241.50  
  Purchase #6 $219.66   3.726%   $227.8445   $227.84   $227.85   $227.80  
  Purchase #7 $238.54   10.269%   $263.0357   $263.04   $263.05   $263.00  
  7 purchase totals = $1,143.49       $1,223.4225   $1,223.41   $1,223.45   $1,223.30