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	$232.86	11.437%	$259.4922	$259.49	$259.50	$259.50
Purchase #2	$116.78	5.627%	$123.3512	$123.35	$123.35	$123.40
Purchase #3	$85.98	6.816%	$91.8404	$91.84	$91.85	$91.80
Purchase #4	$173.74	6.110%	$184.3555	$184.36	$184.35	$184.40
Purchase #5	$89.50	7.722%	$96.4112	$96.41	$96.40	$96.40
Purchase #6	$18.39	11.761%	$20.5528	$20.55	$20.55	$20.60
Purchase #7	$91.98	12.435%	$103.4177	$103.42	$103.40	$103.40
7 purchase totals =	$809.23		$879.4210	$879.42	$879.40	$879.50