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 $87.47   10.483%   $96.6395   $96.64   $96.65   $96.60  
  Purchase #2 $160.55   8.163%   $173.6557   $173.66   $173.65   $173.70  
  Purchase #3 $215.68   3.125%   $222.42   $222.42   $222.40   $222.40  
  Purchase #4 $94.67   3.830%   $98.2959   $98.30   $98.30   $98.30  
  Purchase #5 $30.69   3.187%   $31.6681   $31.67   $31.65   $31.70  
  Purchase #6 $29.98   6.808%   $32.021   $32.02   $32.00   $32.00  
  Purchase #7 $248.77   13.668%   $282.7719   $282.77   $282.75   $282.80  
  7 purchase totals = $867.81       $937.4721   $937.48   $937.40   $937.50