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	$135.32	8.860%	$147.3094	$147.31	$147.30	$147.30
Purchase #2	$24.61	13.278%	$27.8777	$27.88	$27.90	$27.90
Purchase #3	$231.73	13.725%	$263.5349	$263.53	$263.55	$263.50
Purchase #4	$97.88	11.420%	$109.0579	$109.06	$109.05	$109.10
Purchase #5	$221.42	4.742%	$231.9197	$231.92	$231.90	$231.90
Purchase #6	$210.69	13.112%	$238.3157	$238.32	$238.30	$238.30
Purchase #7	$248.44	7.266%	$266.4917	$266.49	$266.50	$266.50
7 purchase totals =	$1,170.09		$1,284.5070	$1,284.51	$1,284.50	$1,284.50