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	$109.65	10.264%	$120.9045	$120.90	$120.90	$120.90
Purchase #2	$99.75	13.760%	$113.4756	$113.48	$113.50	$113.50
Purchase #3	$49.68	12.154%	$55.7181	$55.72	$55.70	$55.70
Purchase #4	$84.25	5.490%	$88.8753	$88.88	$88.90	$88.90
Purchase #5	$109.27	6.375%	$116.236	$116.24	$116.25	$116.20
Purchase #6	$172.55	11.134%	$191.7617	$191.76	$191.75	$191.80
Purchase #7	$161.56	3.312%	$166.9109	$166.91	$166.90	$166.90
7 purchase totals =	$786.71		$853.8821	$853.89	$853.90	$853.90