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	$126.66	9.856%	$139.1436	$139.14	$139.15	$139.10
Purchase #2	$110.89	12.270%	$124.4962	$124.50	$124.50	$124.50
Purchase #3	$149.91	8.231%	$162.2491	$162.25	$162.25	$162.20
Purchase #4	$67.73	6.172%	$71.9103	$71.91	$71.90	$71.90
Purchase #5	$61.97	10.543%	$68.5035	$68.50	$68.50	$68.50
Purchase #6	$61.40	13.400%	$69.6276	$69.63	$69.65	$69.60
Purchase #7	$176.26	11.593%	$196.6938	$196.69	$196.70	$196.70
7 purchase totals =	$754.82		$832.6241	$832.62	$832.65	$832.50