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	$36.41	3.152%	$37.5576	$37.56	$37.55	$37.60
Purchase #2	$160.37	3.689%	$166.286	$166.29	$166.30	$166.30
Purchase #3	$38.85	3.791%	$40.3228	$40.32	$40.30	$40.30
Purchase #4	$86.40	4.625%	$90.396	$90.40	$90.40	$90.40
Purchase #5	$161.69	5.765%	$171.0114	$171.01	$171.00	$171.00
Purchase #6	$143.55	11.390%	$159.9003	$159.90	$159.90	$159.90
Purchase #7	$120.76	3.863%	$125.425	$125.43	$125.45	$125.40
7 purchase totals =	$748.03		$790.8991	$790.91	$790.90	$790.90