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 $241.63   11.515%   $269.4537   $269.45   $269.45   $269.50  
  Purchase #2 $44.46   8.553%   $48.2627   $48.26   $48.25   $48.30  
  Purchase #3 $164.47   3.689%   $170.5373   $170.54   $170.55   $170.50  
  Purchase #4 $220.55   11.497%   $245.9066   $245.91   $245.90   $245.90  
  Purchase #5 $211.44   3.262%   $218.3372   $218.34   $218.35   $218.30  
  Purchase #6 $68.64   12.816%   $77.4369   $77.44   $77.45   $77.40  
  Purchase #7 $68.52   11.347%   $76.295   $76.30   $76.30   $76.30  
  7 purchase totals = $1,019.71       $1,106.2294   $1,106.24   $1,106.25   $1,106.20