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	$6.39	11.771%	$7.1422	$7.14	$7.15	$7.10
Purchase #2	$78.59	12.406%	$88.3399	$88.34	$88.35	$88.30
Purchase #3	$85.97	12.669%	$96.8615	$96.86	$96.85	$96.90
Purchase #4	$107.83	3.801%	$111.9286	$111.93	$111.95	$111.90
Purchase #5	$249.73	11.223%	$277.7572	$277.76	$277.75	$277.80
Purchase #6	$169.78	3.285%	$175.3573	$175.36	$175.35	$175.40
Purchase #7	$124.44	5.650%	$131.4709	$131.47	$131.45	$131.50
7 purchase totals =	$822.73		$888.8576	$888.86	$888.85	$888.90