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	$58.59	11.563%	$65.3648	$65.36	$65.35	$65.40
Purchase #2	$91.81	13.832%	$104.5092	$104.51	$104.50	$104.50
Purchase #3	$155.77	3.345%	$160.9805	$160.98	$161.00	$161.00
Purchase #4	$65.77	11.374%	$73.2507	$73.25	$73.25	$73.30
Purchase #5	$250.86	5.374%	$264.3412	$264.34	$264.35	$264.30
Purchase #6	$9.87	7.637%	$10.6238	$10.62	$10.60	$10.60
Purchase #7	$68.90	5.357%	$72.591	$72.59	$72.60	$72.60
7 purchase totals =	$701.57		$751.6612	$751.65	$751.65	$751.70