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	$73.52	13.664%	$83.5658	$83.57	$83.55	$83.60
Purchase #2	$178.84	7.442%	$192.1493	$192.15	$192.15	$192.10
Purchase #3	$102.59	9.643%	$112.4828	$112.48	$112.50	$112.50
Purchase #4	$14.61	5.801%	$15.4575	$15.46	$15.45	$15.50
Purchase #5	$49.83	5.296%	$52.469	$52.47	$52.45	$52.50
Purchase #6	$209.99	5.296%	$221.1111	$221.11	$221.10	$221.10
Purchase #7	$131.27	12.106%	$147.1615	$147.16	$147.15	$147.20
7 purchase totals =	$760.65		$824.3970	$824.40	$824.35	$824.50