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	$103.78	12.409%	$116.6581	$116.66	$116.65	$116.70
Purchase #2	$228.88	3.725%	$237.4058	$237.41	$237.40	$237.40
Purchase #3	$149.59	11.330%	$166.5385	$166.54	$166.55	$166.50
Purchase #4	$82.91	7.302%	$88.9641	$88.96	$88.95	$89.00
Purchase #5	$189.58	3.869%	$196.9149	$196.91	$196.90	$196.90
Purchase #6	$42.78	10.717%	$47.3647	$47.36	$47.35	$47.40
Purchase #7	$188.66	6.495%	$200.9135	$200.91	$200.90	$200.90
7 purchase totals =	$986.18		$1,054.7596	$1,054.75	$1,054.70	$1,054.80