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 $56.61   4.163%   $58.9667   $58.97   $58.95   $59.00  
  Purchase #2 $216.52   10.540%   $239.3412   $239.34   $239.35   $239.30  
  Purchase #3 $222.81   10.294%   $245.7461   $245.75   $245.75   $245.70  
  Purchase #4 $90.73   13.472%   $102.9531   $102.95   $102.95   $103.00  
  Purchase #5 $77.36   12.151%   $86.76   $86.76   $86.75   $86.80  
  Purchase #6 $69.26   6.628%   $73.8506   $73.85   $73.85   $73.90  
  Purchase #7 $215.48   3.341%   $222.6792   $222.68   $222.70   $222.70  
  7 purchase totals = $948.77       $1,030.2969   $1,030.30   $1,030.30   $1,030.40