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	$178.45	7.188%	$191.277	$191.28	$191.30	$191.30
Purchase #2	$81.35	10.524%	$89.9113	$89.91	$89.90	$89.90
Purchase #3	$244.27	13.114%	$276.3036	$276.30	$276.30	$276.30
Purchase #4	$242.42	8.627%	$263.3336	$263.33	$263.35	$263.30
Purchase #5	$124.40	12.527%	$139.9836	$139.98	$140.00	$140.00
Purchase #6	$49.90	5.185%	$52.4873	$52.49	$52.50	$52.50
Purchase #7	$109.97	8.637%	$119.4681	$119.47	$119.45	$119.50
7 purchase totals =	$1,030.76		$1,132.7645	$1,132.76	$1,132.80	$1,132.80