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	$78.30	10.862%	$86.8049	$86.80	$86.80	$86.80
Purchase #2	$37.33	8.212%	$40.3955	$40.40	$40.40	$40.40
Purchase #3	$136.29	11.867%	$152.4635	$152.46	$152.45	$152.50
Purchase #4	$210.34	13.281%	$238.2753	$238.28	$238.30	$238.30
Purchase #5	$8.38	9.117%	$9.144	$9.14	$9.15	$9.10
Purchase #6	$212.52	13.217%	$240.6088	$240.61	$240.60	$240.60
Purchase #7	$101.43	8.776%	$110.3315	$110.33	$110.35	$110.30
7 purchase totals =	$784.59		$878.0235	$878.02	$878.05	$878.00