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	$106.57	11.176%	$118.4803	$118.48	$118.50	$118.50
Purchase #2	$33.61	11.662%	$37.5296	$37.53	$37.55	$37.50
Purchase #3	$237.75	3.155%	$245.251	$245.25	$245.25	$245.30
Purchase #4	$199.54	9.711%	$218.9173	$218.92	$218.90	$218.90
Purchase #5	$44.49	4.813%	$46.6313	$46.63	$46.65	$46.60
Purchase #6	$45.42	7.218%	$48.6984	$48.70	$48.70	$48.70
Purchase #7	$91.29	8.766%	$99.2925	$99.29	$99.30	$99.30
7 purchase totals =	$758.67		$814.8004	$814.80	$814.85	$814.80