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	$31.99	6.267%	$33.9948	$33.99	$34.00	$34.00
Purchase #2	$233.51	13.175%	$264.2749	$264.27	$264.25	$264.30
Purchase #3	$232.75	13.560%	$264.3109	$264.31	$264.30	$264.30
Purchase #4	$39.69	5.553%	$41.894	$41.89	$41.90	$41.90
Purchase #5	$113.93	13.261%	$129.0383	$129.04	$129.05	$129.00
Purchase #6	$165.36	11.136%	$183.7745	$183.77	$183.75	$183.80
Purchase #7	$114.60	7.814%	$123.5548	$123.55	$123.55	$123.60
7 purchase totals =	$931.83		$1,040.8422	$1,040.82	$1,040.80	$1,040.90