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 $85.32   13.392%   $96.7461   $96.75   $96.75   $96.70  
  Purchase #2 $160.97   10.143%   $177.2972   $177.30   $177.30   $177.30  
  Purchase #3 $52.36   5.220%   $55.0932   $55.09   $55.10   $55.10  
  Purchase #4 $136.55   13.410%   $154.8614   $154.86   $154.85   $154.90  
  Purchase #5 $14.35   5.122%   $15.085   $15.09   $15.10   $15.10  
  Purchase #6 $147.25   4.656%   $154.106   $154.11   $154.10   $154.10  
  Purchase #7 $134.40   13.548%   $152.6085   $152.61   $152.60   $152.60  
  7 purchase totals = $731.20       $805.7974   $805.81   $805.80   $805.80