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	$192.96	6.836%	$206.1507	$206.15	$206.15	$206.20
Purchase #2	$164.34	5.805%	$173.8799	$173.88	$173.90	$173.90
Purchase #3	$162.29	13.684%	$184.4978	$184.50	$184.50	$184.50
Purchase #4	$95.69	11.287%	$106.4905	$106.49	$106.50	$106.50
Purchase #5	$92.51	7.440%	$99.3927	$99.39	$99.40	$99.40
Purchase #6	$37.76	13.628%	$42.9059	$42.91	$42.90	$42.90
Purchase #7	$19.98	12.232%	$22.424	$22.42	$22.40	$22.40
7 purchase totals =	$765.53		$835.7415	$835.74	$835.75	$835.80