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	$76.28	3.445%	$78.9078	$78.91	$78.90	$78.90
Purchase #2	$91.73	13.626%	$104.2291	$104.23	$104.25	$104.20
Purchase #3	$85.56	6.152%	$90.8237	$90.82	$90.80	$90.80
Purchase #4	$170.54	13.399%	$193.3907	$193.39	$193.40	$193.40
Purchase #5	$166.84	5.535%	$176.0746	$176.07	$176.05	$176.10
Purchase #6	$63.52	6.180%	$67.4455	$67.45	$67.45	$67.40
Purchase #7	$237.53	13.260%	$269.0265	$269.03	$269.05	$269.00
7 purchase totals =	$892.00		$979.8979	$979.90	$979.90	$979.80