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	$188.80	4.231%	$196.7881	$196.79	$196.80	$196.80
Purchase #2	$57.48	13.466%	$65.2203	$65.22	$65.20	$65.20
Purchase #3	$28.30	13.728%	$32.185	$32.19	$32.20	$32.20
Purchase #4	$151.59	11.337%	$168.7758	$168.78	$168.80	$168.80
Purchase #5	$78.61	7.566%	$84.5576	$84.56	$84.55	$84.60
Purchase #6	$211.54	5.860%	$223.9362	$223.94	$223.95	$223.90
Purchase #7	$154.69	8.290%	$167.5138	$167.51	$167.50	$167.50
7 purchase totals =	$871.01		$938.9768	$938.99	$939.00	$939.00