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 $61.99   12.639%   $69.8249   $69.82   $69.80   $69.80  
  Purchase #2 $106.27   10.522%   $117.4517   $117.45   $117.45   $117.50  
  Purchase #3 $180.36   7.641%   $194.1413   $194.14   $194.15   $194.10  
  Purchase #4 $32.87   4.113%   $34.2219   $34.22   $34.20   $34.20  
  Purchase #5 $241.33   10.779%   $267.343   $267.34   $267.35   $267.30  
  Purchase #6 $118.94   7.270%   $127.5869   $127.59   $127.60   $127.60  
  Purchase #7 $15.39   3.845%   $15.9817   $15.98   $16.00   $16.00  
  7 purchase totals = $757.15       $826.5514   $826.54   $826.55   $826.50