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	$168.40	12.172%	$188.8976	$188.90	$188.90	$188.90
Purchase #2	$72.84	4.603%	$76.1928	$76.19	$76.20	$76.20
Purchase #3	$128.68	9.585%	$141.014	$141.01	$141.00	$141.00
Purchase #4	$70.61	9.595%	$77.385	$77.39	$77.40	$77.40
Purchase #5	$99.73	4.602%	$104.3196	$104.32	$104.30	$104.30
Purchase #6	$33.58	11.270%	$37.3645	$37.36	$37.35	$37.40
Purchase #7	$154.85	10.636%	$171.3198	$171.32	$171.30	$171.30
7 purchase totals =	$728.69		$796.4933	$796.49	$796.45	$796.50