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	$28.33	4.632%	$29.6422	$29.64	$29.65	$29.60
Purchase #2	$217.85	11.608%	$243.138	$243.14	$243.15	$243.10
Purchase #3	$225.93	13.287%	$255.9493	$255.95	$255.95	$255.90
Purchase #4	$19.96	12.315%	$22.4181	$22.42	$22.40	$22.40
Purchase #5	$204.97	7.115%	$219.5536	$219.55	$219.55	$219.60
Purchase #6	$80.91	10.311%	$89.2526	$89.25	$89.25	$89.30
Purchase #7	$128.89	10.133%	$141.9504	$141.95	$141.95	$142.00
7 purchase totals =	$906.84		$1,001.9042	$1,001.90	$1,001.90	$1,001.90