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	$40.85	11.450%	$45.5273	$45.53	$45.55	$45.50
Purchase #2	$60.92	10.760%	$67.475	$67.48	$67.50	$67.50
Purchase #3	$134.86	10.293%	$148.7411	$148.74	$148.75	$148.70
Purchase #4	$27.47	13.349%	$31.137	$31.14	$31.15	$31.10
Purchase #5	$136.50	13.627%	$155.1009	$155.10	$155.10	$155.10
Purchase #6	$245.90	7.194%	$263.59	$263.59	$263.60	$263.60
Purchase #7	$58.96	3.297%	$60.9039	$60.90	$60.90	$60.90
7 purchase totals =	$705.46		$772.4752	$772.48	$772.55	$772.40