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	$16.38	6.474%	$17.4404	$17.44	$17.45	$17.40
Purchase #2	$171.31	4.706%	$179.3718	$179.37	$179.35	$179.40
Purchase #3	$60.44	11.441%	$67.3549	$67.35	$67.35	$67.40
Purchase #4	$98.89	10.239%	$109.0153	$109.02	$109.00	$109.00
Purchase #5	$192.88	13.265%	$218.4655	$218.47	$218.45	$218.50
Purchase #6	$168.52	6.281%	$179.1047	$179.10	$179.10	$179.10
Purchase #7	$100.64	3.861%	$104.5257	$104.53	$104.55	$104.50
7 purchase totals =	$809.06		$875.2783	$875.28	$875.25	$875.30