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	$141.67	13.535%	$160.845	$160.85	$160.85	$160.80
Purchase #2	$170.39	3.165%	$175.7828	$175.78	$175.80	$175.80
Purchase #3	$148.30	11.115%	$164.7835	$164.78	$164.80	$164.80
Purchase #4	$153.38	11.584%	$171.1475	$171.15	$171.15	$171.10
Purchase #5	$39.32	9.535%	$43.0692	$43.07	$43.05	$43.10
Purchase #6	$236.66	3.742%	$245.5158	$245.52	$245.50	$245.50
Purchase #7	$118.96	8.565%	$129.1489	$129.15	$129.15	$129.10
7 purchase totals =	$1,008.68		$1,090.2927	$1,090.30	$1,090.30	$1,090.20