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	$116.89	6.597%	$124.6012	$124.60	$124.60	$124.60
Purchase #2	$108.69	4.789%	$113.8952	$113.90	$113.90	$113.90
Purchase #3	$17.27	9.404%	$18.8941	$18.89	$18.90	$18.90
Purchase #4	$81.90	9.201%	$89.4356	$89.44	$89.45	$89.40
Purchase #5	$175.32	7.861%	$189.1019	$189.10	$189.10	$189.10
Purchase #6	$67.77	8.505%	$73.5338	$73.53	$73.55	$73.50
Purchase #7	$206.55	4.749%	$216.3591	$216.36	$216.35	$216.40
7 purchase totals =	$774.39		$825.8209	$825.82	$825.85	$825.80