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	$132.66	11.696%	$148.1759	$148.18	$148.20	$148.20
Purchase #2	$175.74	7.272%	$188.5198	$188.52	$188.50	$188.50
Purchase #3	$90.61	9.583%	$99.2932	$99.29	$99.30	$99.30
Purchase #4	$204.46	6.758%	$218.2774	$218.28	$218.30	$218.30
Purchase #5	$7.56	6.266%	$8.0337	$8.03	$8.05	$8.00
Purchase #6	$96.57	13.584%	$109.6881	$109.69	$109.70	$109.70
Purchase #7	$33.95	12.721%	$38.2688	$38.27	$38.25	$38.30
7 purchase totals =	$741.55		$810.2569	$810.26	$810.30	$810.30