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 $172.54   11.293%   $192.0249   $192.02   $192.00   $192.00  
  Purchase #2 $69.63   12.263%   $78.1687   $78.17   $78.15   $78.20  
  Purchase #3 $101.75   13.712%   $115.702   $115.70   $115.70   $115.70  
  Purchase #4 $176.86   3.803%   $183.586   $183.59   $183.60   $183.60  
  Purchase #5 $22.83   9.582%   $25.0176   $25.02   $25.00   $25.00  
  Purchase #6 $128.80   6.230%   $136.8242   $136.82   $136.80   $136.80  
  Purchase #7 $20.92   12.279%   $23.4888   $23.49   $23.50   $23.50  
  7 purchase totals = $693.33       $754.8122   $754.81   $754.75   $754.80