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 $250.41   10.486%   $276.668   $276.67   $276.65   $276.70  
  Purchase #2 $120.48   4.175%   $125.51   $125.51   $125.50   $125.50  
  Purchase #3 $126.70   13.650%   $143.9946   $143.99   $144.00   $144.00  
  Purchase #4 $249.30   11.598%   $278.2138   $278.21   $278.20   $278.20  
  Purchase #5 $90.99   6.356%   $96.7733   $96.77   $96.75   $96.80  
  Purchase #6 $48.41   8.640%   $52.5926   $52.59   $52.60   $52.60  
  Purchase #7 $37.62   12.327%   $42.2574   $42.26   $42.25   $42.30  
  7 purchase totals = $923.91       $1,016.0097   $1,016.00   $1,015.95   $1,016.10