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	$84.35	6.142%	$89.5308	$89.53	$89.55	$89.50
Purchase #2	$96.27	7.351%	$103.3468	$103.35	$103.35	$103.30
Purchase #3	$152.57	13.463%	$173.1105	$173.11	$173.10	$173.10
Purchase #4	$37.79	13.843%	$43.0213	$43.02	$43.00	$43.00
Purchase #5	$228.57	9.525%	$250.3413	$250.34	$250.35	$250.30
Purchase #6	$124.68	12.254%	$139.9583	$139.96	$139.95	$140.00
Purchase #7	$52.59	7.177%	$56.3644	$56.36	$56.35	$56.40
7 purchase totals =	$776.82		$855.6734	$855.67	$855.65	$855.60