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	$33.72	12.475%	$37.9266	$37.93	$37.95	$37.90
Purchase #2	$134.46	5.832%	$142.3017	$142.30	$142.30	$142.30
Purchase #3	$90.31	9.826%	$99.1839	$99.18	$99.20	$99.20
Purchase #4	$11.31	5.747%	$11.96	$11.96	$11.95	$12.00
Purchase #5	$218.89	11.479%	$244.0164	$244.02	$244.00	$244.00
Purchase #6	$199.85	11.167%	$222.1672	$222.17	$222.15	$222.20
Purchase #7	$149.29	10.687%	$165.2446	$165.24	$165.25	$165.20
7 purchase totals =	$837.83		$922.8004	$922.80	$922.80	$922.80