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	$6.33	11.681%	$7.0694	$7.07	$7.05	$7.10
Purchase #2	$25.32	11.812%	$28.3108	$28.31	$28.30	$28.30
Purchase #3	$216.30	13.423%	$245.3339	$245.33	$245.35	$245.30
Purchase #4	$124.54	12.241%	$139.7849	$139.78	$139.80	$139.80
Purchase #5	$233.88	3.247%	$241.4741	$241.47	$241.45	$241.50
Purchase #6	$7.49	5.720%	$7.9184	$7.92	$7.90	$7.90
Purchase #7	$136.78	10.861%	$151.6357	$151.64	$151.65	$151.60
7 purchase totals =	$750.64		$821.5272	$821.52	$821.50	$821.50