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 $61.95   10.744%   $68.6059   $68.61   $68.60   $68.60  
  Purchase #2 $233.45   6.316%   $248.1947   $248.19   $248.20   $248.20  
  Purchase #3 $237.64   3.270%   $245.4108   $245.41   $245.40   $245.40  
  Purchase #4 $66.52   9.124%   $72.5893   $72.59   $72.60   $72.60  
  Purchase #5 $215.38   13.526%   $244.5123   $244.51   $244.50   $244.50  
  Purchase #6 $9.26   5.517%   $9.7709   $9.77   $9.75   $9.80  
  Purchase #7 $113.34   11.659%   $126.5543   $126.55   $126.55   $126.60  
  7 purchase totals = $937.54       $1,015.6382   $1,015.63   $1,015.60   $1,015.70