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	$52.28	13.343%	$59.2557	$59.26	$59.25	$59.30
Purchase #2	$124.76	5.788%	$131.9811	$131.98	$132.00	$132.00
Purchase #3	$186.50	6.277%	$198.2066	$198.21	$198.20	$198.20
Purchase #4	$111.89	7.569%	$120.359	$120.36	$120.35	$120.40
Purchase #5	$84.98	6.147%	$90.2037	$90.20	$90.20	$90.20
Purchase #6	$51.77	8.242%	$56.0369	$56.04	$56.05	$56.00
Purchase #7	$172.82	7.219%	$185.2959	$185.30	$185.30	$185.30
7 purchase totals =	$785.00		$841.3389	$841.35	$841.35	$841.40