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 $63.41   7.154%   $67.9464   $67.95   $67.95   $67.90  
  Purchase #2 $114.86   11.122%   $127.6347   $127.63   $127.65   $127.60  
  Purchase #3 $76.55   5.359%   $80.6523   $80.65   $80.65   $80.70  
  Purchase #4 $177.66   8.590%   $192.921   $192.92   $192.90   $192.90  
  Purchase #5 $139.84   8.553%   $151.8005   $151.80   $151.80   $151.80  
  Purchase #6 $207.97   11.104%   $231.063   $231.06   $231.05   $231.10  
  Purchase #7 $211.40   13.618%   $240.1885   $240.19   $240.20   $240.20  
  7 purchase totals = $991.69       $1,092.2064   $1,092.20   $1,092.20   $1,092.20