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	$104.69	4.177%	$109.0629	$109.06	$109.05	$109.10
Purchase #2	$162.54	7.592%	$174.88	$174.88	$174.90	$174.90
Purchase #3	$102.53	9.766%	$112.5431	$112.54	$112.55	$112.50
Purchase #4	$64.74	11.583%	$72.2388	$72.24	$72.25	$72.20
Purchase #5	$18.41	8.770%	$20.0246	$20.02	$20.00	$20.00
Purchase #6	$19.42	12.872%	$21.9197	$21.92	$21.90	$21.90
Purchase #7	$35.73	13.486%	$40.5485	$40.55	$40.55	$40.50
7 purchase totals =	$508.06		$551.2176	$551.21	$551.20	$551.10