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 $55.74   4.382%   $58.1825   $58.18   $58.20   $58.20  
  Purchase #2 $228.80   5.861%   $242.21   $242.21   $242.20   $242.20  
  Purchase #3 $50.87   6.487%   $54.1699   $54.17   $54.15   $54.20  
  Purchase #4 $191.58   5.427%   $201.977   $201.98   $202.00   $202.00  
  Purchase #5 $95.26   13.212%   $107.8458   $107.85   $107.85   $107.80  
  Purchase #6 $213.57   8.160%   $230.9973   $231.00   $231.00   $231.00  
  Purchase #7 $228.91   8.712%   $248.8526   $248.85   $248.85   $248.90  
  7 purchase totals = $1,064.73       $1,144.2351   $1,144.24   $1,144.25   $1,144.30