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 $142.64   13.732%   $162.2273   $162.23   $162.25   $162.20  
  Purchase #2 $230.95   3.394%   $238.7884   $238.79   $238.80   $238.80  
  Purchase #3 $107.66   6.456%   $114.6105   $114.61   $114.60   $114.60  
  Purchase #4 $97.57   9.591%   $106.9279   $106.93   $106.95   $106.90  
  Purchase #5 $115.25   4.859%   $120.85   $120.85   $120.85   $120.90  
  Purchase #6 $64.68   8.225%   $69.9999   $70.00   $70.00   $70.00  
  Purchase #7 $92.73   12.784%   $104.5846   $104.58   $104.60   $104.60  
  7 purchase totals = $851.48       $917.9886   $917.99   $918.05   $918.00