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 $234.65   13.797%   $267.0247   $267.02   $267.00   $267.00  
  Purchase #2 $184.56   4.147%   $192.2137   $192.21   $192.20   $192.20  
  Purchase #3 $52.69   7.162%   $56.4637   $56.46   $56.45   $56.50  
  Purchase #4 $106.95   12.580%   $120.4043   $120.40   $120.40   $120.40  
  Purchase #5 $123.83   8.287%   $134.0918   $134.09   $134.10   $134.10  
  Purchase #6 $245.33   6.163%   $260.4497   $260.45   $260.45   $260.40  
  Purchase #7 $122.50   13.401%   $138.9162   $138.92   $138.90   $138.90  
  7 purchase totals = $1,070.51       $1,169.5641   $1,169.55   $1,169.50   $1,169.50