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 $66.26   5.168%   $69.6843   $69.68   $69.70   $69.70  
  Purchase #2 $201.55   6.358%   $214.3645   $214.36   $214.35   $214.40  
  Purchase #3 $169.64   9.641%   $185.995   $186.00   $186.00   $186.00  
  Purchase #4 $79.29   3.222%   $81.8447   $81.84   $81.85   $81.80  
  Purchase #5 $98.67   9.149%   $107.6973   $107.70   $107.70   $107.70  
  Purchase #6 $107.37   3.634%   $111.2718   $111.27   $111.25   $111.30  
  Purchase #7 $205.39   7.575%   $220.9483   $220.95   $220.95   $220.90  
  7 purchase totals = $928.17       $991.8059   $991.80   $991.80   $991.80