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 $11.97   9.287%   $13.0817   $13.08   $13.10   $13.10  
  Purchase #2 $26.59   6.654%   $28.3593   $28.36   $28.35   $28.40  
  Purchase #3 $99.64   5.452%   $105.0724   $105.07   $105.05   $105.10  
  Purchase #4 $76.77   7.754%   $82.7227   $82.72   $82.70   $82.70  
  Purchase #5 $134.83   4.716%   $141.1886   $141.19   $141.20   $141.20  
  Purchase #6 $101.47   13.780%   $115.4526   $115.45   $115.45   $115.50  
  Purchase #7 $178.78   10.422%   $197.4125   $197.41   $197.40   $197.40  
  7 purchase totals = $630.05       $683.2898   $683.28   $683.25   $683.40