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	$99.41	8.397%	$107.7575	$107.76	$107.75	$107.80
Purchase #2	$79.89	6.585%	$85.1508	$85.15	$85.15	$85.20
Purchase #3	$137.88	10.179%	$151.9148	$151.91	$151.90	$151.90
Purchase #4	$179.67	3.251%	$185.5111	$185.51	$185.50	$185.50
Purchase #5	$231.84	12.289%	$260.3308	$260.33	$260.35	$260.30
Purchase #6	$250.85	13.787%	$285.4347	$285.43	$285.45	$285.40
Purchase #7	$135.32	6.681%	$144.3607	$144.36	$144.35	$144.40
7 purchase totals =	$1,114.86		$1,220.4604	$1,220.45	$1,220.45	$1,220.50