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	$31.31	3.338%	$32.3551	$32.36	$32.35	$32.40
Purchase #2	$92.42	7.791%	$99.6204	$99.62	$99.60	$99.60
Purchase #3	$107.98	11.245%	$120.1224	$120.12	$120.10	$120.10
Purchase #4	$176.88	9.240%	$193.2237	$193.22	$193.20	$193.20
Purchase #5	$73.77	11.721%	$82.4166	$82.42	$82.40	$82.40
Purchase #6	$190.46	11.432%	$212.2334	$212.23	$212.25	$212.20
Purchase #7	$162.87	7.119%	$174.4647	$174.46	$174.45	$174.50
7 purchase totals =	$835.69		$914.4363	$914.43	$914.35	$914.40