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	$25.43	11.790%	$28.4282	$28.43	$28.45	$28.40
Purchase #2	$90.31	5.338%	$95.1307	$95.13	$95.15	$95.10
Purchase #3	$154.75	6.258%	$164.4343	$164.43	$164.45	$164.40
Purchase #4	$135.53	8.856%	$147.5325	$147.53	$147.55	$147.50
Purchase #5	$101.98	7.841%	$109.9763	$109.98	$110.00	$110.00
Purchase #6	$98.73	13.562%	$112.1198	$112.12	$112.10	$112.10
Purchase #7	$53.86	12.789%	$60.7482	$60.75	$60.75	$60.70
7 purchase totals =	$660.59		$718.3700	$718.37	$718.45	$718.20