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	$240.98	6.146%	$255.7906	$255.79	$255.80	$255.80
Purchase #2	$89.34	10.787%	$98.9771	$98.98	$99.00	$99.00
Purchase #3	$185.43	13.212%	$209.929	$209.93	$209.95	$209.90
Purchase #4	$56.53	11.167%	$62.8427	$62.84	$62.85	$62.80
Purchase #5	$82.76	3.814%	$85.9165	$85.92	$85.90	$85.90
Purchase #6	$228.51	4.649%	$239.1334	$239.13	$239.15	$239.10
Purchase #7	$83.44	10.651%	$92.3272	$92.33	$92.35	$92.30
7 purchase totals =	$966.99		$1,044.9165	$1,044.92	$1,045.00	$1,044.80