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	$30.49	5.214%	$32.0797	$32.08	$32.10	$32.10
Purchase #2	$53.54	3.452%	$55.3882	$55.39	$55.40	$55.40
Purchase #3	$29.96	7.764%	$32.2861	$32.29	$32.30	$32.30
Purchase #4	$29.88	8.380%	$32.3839	$32.38	$32.40	$32.40
Purchase #5	$20.69	7.864%	$22.3171	$22.32	$22.30	$22.30
Purchase #6	$226.56	7.480%	$243.5067	$243.51	$243.50	$243.50
Purchase #7	$239.38	6.731%	$255.4927	$255.49	$255.50	$255.50
7 purchase totals =	$630.50		$673.4544	$673.46	$673.50	$673.50