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 $49.85   4.348%   $52.0175   $52.02   $52.00   $52.00  
  Purchase #2 $240.71   10.715%   $266.5021   $266.50   $266.50   $266.50  
  Purchase #3 $164.45   6.761%   $175.5685   $175.57   $175.55   $175.60  
  Purchase #4 $152.43   12.186%   $171.0051   $171.01   $171.00   $171.00  
  Purchase #5 $168.61   9.541%   $184.6971   $184.70   $184.70   $184.70  
  Purchase #6 $185.86   13.828%   $211.5607   $211.56   $211.55   $211.60  
  Purchase #7 $90.47   12.769%   $102.0221   $102.02   $102.00   $102.00  
  7 purchase totals = $1,052.38       $1,163.3731   $1,163.38   $1,163.30   $1,163.40