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 $46.82   10.157%   $51.5755   $51.58   $51.60   $51.60  
  Purchase #2 $233.74   4.688%   $244.6977   $244.70   $244.70   $244.70  
  Purchase #3 $198.58   4.844%   $208.1992   $208.20   $208.20   $208.20  
  Purchase #4 $117.89   11.787%   $131.7857   $131.79   $131.80   $131.80  
  Purchase #5 $160.51   9.445%   $175.6702   $175.67   $175.65   $175.70  
  Purchase #6 $114.36   9.260%   $124.9497   $124.95   $124.95   $124.90  
  Purchase #7 $234.88   13.287%   $266.0885   $266.09   $266.10   $266.10  
  7 purchase totals = $1,106.78       $1,202.9665   $1,202.98   $1,203.00   $1,203.00