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	$166.78	11.450%	$185.8763	$185.88	$185.90	$185.90
Purchase #2	$111.56	6.554%	$118.8716	$118.87	$118.85	$118.90
Purchase #3	$79.46	8.561%	$86.2626	$86.26	$86.25	$86.30
Purchase #4	$215.78	7.597%	$232.1728	$232.17	$232.15	$232.20
Purchase #5	$93.30	7.491%	$100.2891	$100.29	$100.30	$100.30
Purchase #6	$37.36	7.385%	$40.119	$40.12	$40.10	$40.10
Purchase #7	$26.71	6.302%	$28.3933	$28.39	$28.40	$28.40
7 purchase totals =	$730.95		$791.9847	$791.98	$791.95	$792.10