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	$169.97	11.332%	$189.231	$189.23	$189.25	$189.20
Purchase #2	$149.45	10.333%	$164.8927	$164.89	$164.90	$164.90
Purchase #3	$244.59	12.531%	$275.2396	$275.24	$275.25	$275.20
Purchase #4	$53.90	3.343%	$55.7019	$55.70	$55.70	$55.70
Purchase #5	$155.97	3.154%	$160.8893	$160.89	$160.90	$160.90
Purchase #6	$133.95	6.111%	$142.1357	$142.14	$142.15	$142.10
Purchase #7	$85.29	9.812%	$93.6587	$93.66	$93.65	$93.70
7 purchase totals =	$993.12		$1,081.7489	$1,081.75	$1,081.80	$1,081.70