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	$71.89	12.228%	$80.6807	$80.68	$80.70	$80.70
Purchase #2	$156.52	10.743%	$173.3349	$173.33	$173.35	$173.30
Purchase #3	$105.78	7.141%	$113.3337	$113.33	$113.35	$113.30
Purchase #4	$58.68	4.503%	$61.3224	$61.32	$61.30	$61.30
Purchase #5	$60.41	5.742%	$63.8787	$63.88	$63.90	$63.90
Purchase #6	$36.30	5.512%	$38.3009	$38.30	$38.30	$38.30
Purchase #7	$196.79	9.606%	$215.6936	$215.69	$215.70	$215.70
7 purchase totals =	$686.37		$746.5449	$746.53	$746.60	$746.50