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	$80.94	12.717%	$91.2331	$91.23	$91.25	$91.20
Purchase #2	$20.27	9.421%	$22.1796	$22.18	$22.20	$22.20
Purchase #3	$10.93	12.690%	$12.317	$12.32	$12.30	$12.30
Purchase #4	$18.85	13.123%	$21.3237	$21.32	$21.30	$21.30
Purchase #5	$28.83	11.176%	$32.052	$32.05	$32.05	$32.10
Purchase #6	$165.56	11.789%	$185.0779	$185.08	$185.10	$185.10
Purchase #7	$53.61	9.326%	$58.6097	$58.61	$58.60	$58.60
7 purchase totals =	$378.99		$422.7930	$422.79	$422.80	$422.80