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	$233.74	10.711%	$258.7759	$258.78	$258.80	$258.80
Purchase #2	$78.91	13.561%	$89.611	$89.61	$89.60	$89.60
Purchase #3	$215.46	4.372%	$224.8799	$224.88	$224.90	$224.90
Purchase #4	$29.47	5.707%	$31.1519	$31.15	$31.15	$31.20
Purchase #5	$12.60	4.674%	$13.1889	$13.19	$13.20	$13.20
Purchase #6	$73.52	12.396%	$82.6335	$82.63	$82.65	$82.60
Purchase #7	$213.66	9.764%	$234.5218	$234.52	$234.50	$234.50
7 purchase totals =	$857.36		$934.7629	$934.76	$934.80	$934.80