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	$107.27	13.261%	$121.4951	$121.50	$121.50	$121.50
Purchase #2	$184.42	3.648%	$191.1476	$191.15	$191.15	$191.10
Purchase #3	$88.54	9.138%	$96.6308	$96.63	$96.65	$96.60
Purchase #4	$226.86	5.561%	$239.4757	$239.48	$239.50	$239.50
Purchase #5	$142.66	6.225%	$151.5406	$151.54	$151.55	$151.50
Purchase #6	$125.71	6.695%	$134.1263	$134.13	$134.15	$134.10
Purchase #7	$127.95	11.474%	$142.631	$142.63	$142.65	$142.60
7 purchase totals =	$1,003.41		$1,077.0471	$1,077.06	$1,077.15	$1,076.90