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	$146.78	13.320%	$166.3311	$166.33	$166.35	$166.30
Purchase #2	$56.28	9.563%	$61.6621	$61.66	$61.65	$61.70
Purchase #3	$208.29	8.135%	$225.2344	$225.23	$225.25	$225.20
Purchase #4	$35.50	13.468%	$40.2811	$40.28	$40.30	$40.30
Purchase #5	$104.70	5.454%	$110.4103	$110.41	$110.40	$110.40
Purchase #6	$222.66	12.537%	$250.5749	$250.57	$250.55	$250.60
Purchase #7	$155.82	10.174%	$171.6731	$171.67	$171.65	$171.70
7 purchase totals =	$930.03		$1,026.1670	$1,026.15	$1,026.15	$1,026.20