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	$72.96	9.346%	$79.7788	$79.78	$79.80	$79.80
Purchase #2	$39.64	13.827%	$45.121	$45.12	$45.10	$45.10
Purchase #3	$94.41	6.113%	$100.1813	$100.18	$100.20	$100.20
Purchase #4	$17.54	6.770%	$18.7275	$18.73	$18.75	$18.70
Purchase #5	$206.57	4.441%	$215.7438	$215.74	$215.75	$215.70
Purchase #6	$170.33	7.361%	$182.868	$182.87	$182.85	$182.90
Purchase #7	$150.52	11.517%	$167.8554	$167.86	$167.85	$167.90
7 purchase totals =	$751.97		$810.2758	$810.28	$810.30	$810.30