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	$203.90	3.380%	$210.7918	$210.79	$210.80	$210.80
Purchase #2	$56.46	11.767%	$63.1036	$63.10	$63.10	$63.10
Purchase #3	$137.78	12.580%	$155.1127	$155.11	$155.10	$155.10
Purchase #4	$99.27	4.781%	$104.0161	$104.02	$104.00	$104.00
Purchase #5	$202.65	9.837%	$222.5847	$222.58	$222.60	$222.60
Purchase #6	$119.79	6.360%	$127.4086	$127.41	$127.40	$127.40
Purchase #7	$187.72	10.431%	$207.3011	$207.30	$207.30	$207.30
7 purchase totals =	$1,007.57		$1,090.3186	$1,090.31	$1,090.30	$1,090.30