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 $51.46   8.771%   $55.9736   $55.97   $55.95   $56.00  
  Purchase #2 $228.67   10.347%   $252.3305   $252.33   $252.35   $252.30  
  Purchase #3 $121.81   6.199%   $129.361   $129.36   $129.35   $129.40  
  Purchase #4 $242.65   13.342%   $275.0244   $275.02   $275.00   $275.00  
  Purchase #5 $114.58   13.165%   $129.6645   $129.66   $129.65   $129.70  
  Purchase #6 $174.35   10.725%   $193.049   $193.05   $193.05   $193.00  
  Purchase #7 $33.98   5.151%   $35.7303   $35.73   $35.75   $35.70  
  7 purchase totals = $967.50       $1,071.1333   $1,071.12   $1,071.10   $1,071.10