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 $93.48   12.331%   $105.007   $105.01   $105.00   $105.00  
  Purchase #2 $226.59   5.240%   $238.4633   $238.46   $238.45   $238.50  
  Purchase #3 $222.99   13.451%   $252.9844   $252.98   $253.00   $253.00  
  Purchase #4 $182.63   13.550%   $207.3764   $207.38   $207.40   $207.40  
  Purchase #5 $144.48   10.679%   $159.909   $159.91   $159.90   $159.90  
  Purchase #6 $30.37   13.553%   $34.486   $34.49   $34.50   $34.50  
  Purchase #7 $178.34   13.107%   $201.715   $201.72   $201.70   $201.70  
  7 purchase totals = $1,078.88       $1,199.9411   $1,199.95   $1,199.95   $1,200.00