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	$72.90	13.555%	$82.7816	$82.78	$82.80	$82.80
Purchase #2	$225.65	3.555%	$233.6719	$233.67	$233.65	$233.70
Purchase #3	$206.69	10.478%	$228.347	$228.35	$228.35	$228.30
Purchase #4	$108.76	9.306%	$118.8812	$118.88	$118.90	$118.90
Purchase #5	$43.43	5.608%	$45.8656	$45.87	$45.85	$45.90
Purchase #6	$249.41	11.465%	$278.0049	$278.00	$278.00	$278.00
Purchase #7	$23.99	3.305%	$24.7829	$24.78	$24.80	$24.80
7 purchase totals =	$930.83		$1,012.3351	$1,012.33	$1,012.35	$1,012.40