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	$212.89	5.354%	$224.2881	$224.29	$224.30	$224.30
Purchase #2	$208.86	12.154%	$234.2448	$234.24	$234.25	$234.20
Purchase #3	$175.76	11.819%	$196.5331	$196.53	$196.55	$196.50
Purchase #4	$110.38	6.285%	$117.3174	$117.32	$117.30	$117.30
Purchase #5	$18.54	6.135%	$19.6774	$19.68	$19.70	$19.70
Purchase #6	$82.55	3.140%	$85.1421	$85.14	$85.15	$85.10
Purchase #7	$92.88	12.315%	$104.3182	$104.32	$104.30	$104.30
7 purchase totals =	$901.86		$981.5211	$981.52	$981.55	$981.40