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	$84.36	4.732%	$88.3519	$88.35	$88.35	$88.40
Purchase #2	$99.32	3.791%	$103.0852	$103.09	$103.10	$103.10
Purchase #3	$38.37	11.362%	$42.7296	$42.73	$42.75	$42.70
Purchase #4	$213.67	9.583%	$234.146	$234.15	$234.15	$234.10
Purchase #5	$113.80	11.781%	$127.2068	$127.21	$127.20	$127.20
Purchase #6	$72.91	10.471%	$80.5444	$80.54	$80.55	$80.50
Purchase #7	$88.47	13.760%	$100.6435	$100.64	$100.65	$100.60
7 purchase totals =	$710.90		$776.7074	$776.71	$776.75	$776.60