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 $81.83   5.270%   $86.1424   $86.14   $86.15   $86.10  
  Purchase #2 $248.35   9.137%   $271.0417   $271.04   $271.05   $271.00  
  Purchase #3 $42.44   4.145%   $44.1991   $44.20   $44.20   $44.20  
  Purchase #4 $49.63   12.325%   $55.7469   $55.75   $55.75   $55.70  
  Purchase #5 $71.34   4.818%   $74.7772   $74.78   $74.80   $74.80  
  Purchase #6 $97.34   4.363%   $101.5869   $101.59   $101.60   $101.60  
  Purchase #7 $139.78   13.322%   $158.4015   $158.40   $158.40   $158.40  
  7 purchase totals = $730.71       $791.8957   $791.90   $791.95   $791.80