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	$155.85	11.836%	$174.2964	$174.30	$174.30	$174.30
Purchase #2	$154.88	10.270%	$170.7862	$170.79	$170.80	$170.80
Purchase #3	$232.41	11.144%	$258.3098	$258.31	$258.30	$258.30
Purchase #4	$42.63	7.624%	$45.8801	$45.88	$45.90	$45.90
Purchase #5	$185.98	12.334%	$208.9188	$208.92	$208.90	$208.90
Purchase #6	$127.45	7.329%	$136.7908	$136.79	$136.80	$136.80
Purchase #7	$96.32	3.729%	$99.9118	$99.91	$99.90	$99.90
7 purchase totals =	$995.52		$1,094.8939	$1,094.90	$1,094.90	$1,094.90