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	$37.98	6.301%	$40.3731	$40.37	$40.35	$40.40
Purchase #2	$230.94	11.203%	$256.8122	$256.81	$256.80	$256.80
Purchase #3	$219.64	13.689%	$249.7065	$249.71	$249.70	$249.70
Purchase #4	$162.33	4.802%	$170.1251	$170.13	$170.15	$170.10
Purchase #5	$144.32	4.759%	$151.1882	$151.19	$151.20	$151.20
Purchase #6	$138.90	4.653%	$145.363	$145.36	$145.35	$145.40
Purchase #7	$76.87	13.427%	$87.1913	$87.19	$87.20	$87.20
7 purchase totals =	$1,010.98		$1,100.7594	$1,100.76	$1,100.75	$1,100.80