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 $63.95   4.743%   $66.9831   $66.98   $67.00   $67.00  
  Purchase #2 $223.80   7.820%   $241.3012   $241.30   $241.30   $241.30  
  Purchase #3 $186.65   9.340%   $204.0831   $204.08   $204.10   $204.10  
  Purchase #4 $37.27   11.387%   $41.5139   $41.51   $41.50   $41.50  
  Purchase #5 $97.38   10.466%   $107.5718   $107.57   $107.55   $107.60  
  Purchase #6 $208.87   8.420%   $226.4569   $226.46   $226.45   $226.50  
  Purchase #7 $21.82   6.778%   $23.299   $23.30   $23.30   $23.30  
  7 purchase totals = $839.74       $911.2090   $911.20   $911.20   $911.30