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	$90.54	9.819%	$99.4301	$99.43	$99.45	$99.40
Purchase #2	$30.99	13.824%	$35.2741	$35.27	$35.25	$35.30
Purchase #3	$25.51	9.521%	$27.9388	$27.94	$27.95	$27.90
Purchase #4	$161.54	13.798%	$183.8293	$183.83	$183.85	$183.80
Purchase #5	$75.74	10.557%	$83.7359	$83.74	$83.75	$83.70
Purchase #6	$220.46	3.172%	$227.453	$227.45	$227.45	$227.50
Purchase #7	$82.73	4.211%	$86.2138	$86.21	$86.20	$86.20
7 purchase totals =	$687.51		$743.8750	$743.87	$743.90	$743.80