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 $74.61   11.652%   $83.3036   $83.30   $83.30   $83.30  
  Purchase #2 $230.94   4.429%   $241.1683   $241.17   $241.15   $241.20  
  Purchase #3 $200.66   4.106%   $208.8991   $208.90   $208.90   $208.90  
  Purchase #4 $245.52   3.779%   $254.7982   $254.80   $254.80   $254.80  
  Purchase #5 $227.96   4.248%   $237.6437   $237.64   $237.65   $237.60  
  Purchase #6 $105.54   6.850%   $112.7695   $112.77   $112.75   $112.80  
  Purchase #7 $214.77   3.481%   $222.2461   $222.25   $222.25   $222.20  
  7 purchase totals = $1,300.00       $1,360.8285   $1,360.83   $1,360.80   $1,360.80