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 $50.78   12.149%   $56.9493   $56.95   $56.95   $56.90  
  Purchase #2 $232.91   5.482%   $245.6781   $245.68   $245.70   $245.70  
  Purchase #3 $219.36   5.524%   $231.4774   $231.48   $231.50   $231.50  
  Purchase #4 $231.86   8.615%   $251.8347   $251.83   $251.85   $251.80  
  Purchase #5 $86.38   7.698%   $93.0295   $93.03   $93.05   $93.00  
  Purchase #6 $224.44   7.585%   $241.4638   $241.46   $241.45   $241.50  
  Purchase #7 $226.28   4.386%   $236.2046   $236.20   $236.20   $236.20  
  7 purchase totals = $1,272.01       $1,356.6374   $1,356.63   $1,356.70   $1,356.60