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 $87.34   10.366%   $96.3937   $96.39   $96.40   $96.40  
  Purchase #2 $104.95   6.106%   $111.3582   $111.36   $111.35   $111.40  
  Purchase #3 $178.86   7.669%   $192.5768   $192.58   $192.60   $192.60  
  Purchase #4 $40.34   6.121%   $42.8092   $42.81   $42.80   $42.80  
  Purchase #5 $250.97   9.585%   $275.0255   $275.03   $275.05   $275.00  
  Purchase #6 $43.81   5.508%   $46.2231   $46.22   $46.20   $46.20  
  Purchase #7 $147.74   5.381%   $155.6899   $155.69   $155.70   $155.70  
  7 purchase totals = $854.01       $920.0764   $920.08   $920.10   $920.10