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	$47.32	12.568%	$53.2672	$53.27	$53.25	$53.30
Purchase #2	$186.87	11.848%	$209.0104	$209.01	$209.00	$209.00
Purchase #3	$168.95	12.370%	$189.8491	$189.85	$189.85	$189.80
Purchase #4	$48.81	10.495%	$53.9326	$53.93	$53.95	$53.90
Purchase #5	$198.86	5.624%	$210.0439	$210.04	$210.05	$210.00
Purchase #6	$89.73	7.578%	$96.5297	$96.53	$96.55	$96.50
Purchase #7	$128.29	11.440%	$142.9664	$142.97	$142.95	$143.00
7 purchase totals =	$868.83		$955.5993	$955.60	$955.60	$955.50