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	$155.42	5.817%	$164.4608	$164.46	$164.45	$164.50
Purchase #2	$167.73	11.498%	$187.0156	$187.02	$187.00	$187.00
Purchase #3	$233.42	8.440%	$253.1206	$253.12	$253.10	$253.10
Purchase #4	$46.41	4.628%	$48.5579	$48.56	$48.55	$48.60
Purchase #5	$98.87	12.382%	$111.1121	$111.11	$111.10	$111.10
Purchase #6	$8.88	13.499%	$10.0787	$10.08	$10.10	$10.10
Purchase #7	$151.33	3.668%	$156.8808	$156.88	$156.90	$156.90
7 purchase totals =	$862.06		$931.2265	$931.23	$931.20	$931.30