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	$233.50	7.227%	$250.375	$250.38	$250.40	$250.40
Purchase #2	$81.33	13.495%	$92.3055	$92.31	$92.30	$92.30
Purchase #3	$75.29	13.541%	$85.485	$85.49	$85.50	$85.50
Purchase #4	$190.55	10.463%	$210.4872	$210.49	$210.50	$210.50
Purchase #5	$234.94	10.233%	$258.9814	$258.98	$259.00	$259.00
Purchase #6	$6.98	13.235%	$7.9038	$7.90	$7.90	$7.90
Purchase #7	$174.72	6.152%	$185.4688	$185.47	$185.45	$185.50
7 purchase totals =	$997.31		$1,091.0067	$1,091.02	$1,091.05	$1,091.10