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	$75.69	10.119%	$83.3491	$83.35	$83.35	$83.30
Purchase #2	$20.73	8.503%	$22.4927	$22.49	$22.50	$22.50
Purchase #3	$176.50	4.393%	$184.2536	$184.25	$184.25	$184.30
Purchase #4	$229.96	8.857%	$250.3276	$250.33	$250.35	$250.30
Purchase #5	$103.90	7.703%	$111.9034	$111.90	$111.90	$111.90
Purchase #6	$89.63	11.272%	$99.7331	$99.73	$99.75	$99.70
Purchase #7	$191.90	13.642%	$218.079	$218.08	$218.10	$218.10
7 purchase totals =	$888.31		$970.1385	$970.13	$970.20	$970.10