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	$38.45	5.285%	$40.4821	$40.48	$40.50	$40.50
Purchase #2	$91.79	8.376%	$99.4783	$99.48	$99.50	$99.50
Purchase #3	$140.66	7.322%	$150.9591	$150.96	$150.95	$151.00
Purchase #4	$206.86	4.773%	$216.7334	$216.73	$216.75	$216.70
Purchase #5	$130.38	13.686%	$148.2238	$148.22	$148.20	$148.20
Purchase #6	$241.97	3.399%	$250.1946	$250.19	$250.20	$250.20
Purchase #7	$152.55	5.337%	$160.6916	$160.69	$160.70	$160.70
7 purchase totals =	$1,002.66		$1,066.7629	$1,066.75	$1,066.80	$1,066.80