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	$86.77	4.773%	$90.9115	$90.91	$90.90	$90.90
Purchase #2	$96.60	3.265%	$99.754	$99.75	$99.75	$99.80
Purchase #3	$56.66	8.438%	$61.441	$61.44	$61.45	$61.40
Purchase #4	$107.33	3.227%	$110.7935	$110.79	$110.80	$110.80
Purchase #5	$244.72	13.678%	$278.1928	$278.19	$278.20	$278.20
Purchase #6	$191.39	7.844%	$206.4026	$206.40	$206.40	$206.40
Purchase #7	$54.35	9.296%	$59.4024	$59.40	$59.40	$59.40
7 purchase totals =	$837.82		$906.8978	$906.88	$906.90	$906.90