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	$178.52	6.138%	$189.4776	$189.48	$189.50	$189.50
Purchase #2	$104.43	6.367%	$111.0791	$111.08	$111.10	$111.10
Purchase #3	$210.91	7.818%	$227.3989	$227.40	$227.40	$227.40
Purchase #4	$67.69	11.350%	$75.3728	$75.37	$75.35	$75.40
Purchase #5	$36.72	12.700%	$41.3834	$41.38	$41.40	$41.40
Purchase #6	$139.64	10.212%	$153.9	$153.90	$153.90	$153.90
Purchase #7	$231.36	5.779%	$244.7303	$244.73	$244.75	$244.70
7 purchase totals =	$969.27		$1,043.3421	$1,043.34	$1,043.40	$1,043.40