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 $68.66   3.344%   $70.956   $70.96   $70.95   $71.00  
  Purchase #2 $204.55   8.846%   $222.6445   $222.64   $222.65   $222.60  
  Purchase #3 $245.67   8.258%   $265.9574   $265.96   $265.95   $266.00  
  Purchase #4 $197.68   4.122%   $205.8284   $205.83   $205.85   $205.80  
  Purchase #5 $43.69   10.712%   $48.3701   $48.37   $48.35   $48.40  
  Purchase #6 $28.83   9.683%   $31.6216   $31.62   $31.60   $31.60  
  Purchase #7 $104.25   8.680%   $113.2989   $113.30   $113.30   $113.30  
  7 purchase totals = $893.33       $958.6769   $958.68   $958.65   $958.70