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	$82.64	9.269%	$90.2999	$90.30	$90.30	$90.30
Purchase #2	$76.92	7.851%	$82.959	$82.96	$82.95	$83.00
Purchase #3	$96.75	13.272%	$109.5907	$109.59	$109.60	$109.60
Purchase #4	$124.94	6.455%	$133.0049	$133.00	$133.00	$133.00
Purchase #5	$215.99	11.306%	$240.4098	$240.41	$240.40	$240.40
Purchase #6	$215.57	4.447%	$225.1564	$225.16	$225.15	$225.20
Purchase #7	$35.31	13.474%	$40.0677	$40.07	$40.05	$40.10
7 purchase totals =	$848.12		$921.4884	$921.49	$921.45	$921.60