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	$206.84	13.372%	$234.4986	$234.50	$234.50	$234.50
Purchase #2	$96.70	3.130%	$99.7267	$99.73	$99.75	$99.70
Purchase #3	$100.34	10.547%	$110.9229	$110.92	$110.90	$110.90
Purchase #4	$82.77	13.479%	$93.9266	$93.93	$93.95	$93.90
Purchase #5	$16.44	12.712%	$18.5299	$18.53	$18.55	$18.50
Purchase #6	$225.78	13.155%	$255.4814	$255.48	$255.50	$255.50
Purchase #7	$219.31	13.194%	$248.2458	$248.25	$248.25	$248.20
7 purchase totals =	$948.18		$1,061.3319	$1,061.34	$1,061.40	$1,061.20