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	$104.39	11.332%	$116.2195	$116.22	$116.20	$116.20
Purchase #2	$90.30	8.572%	$98.0405	$98.04	$98.05	$98.00
Purchase #3	$175.56	9.207%	$191.7238	$191.72	$191.70	$191.70
Purchase #4	$127.34	13.810%	$144.9257	$144.93	$144.95	$144.90
Purchase #5	$102.39	7.361%	$109.9269	$109.93	$109.95	$109.90
Purchase #6	$233.48	6.698%	$249.1185	$249.12	$249.10	$249.10
Purchase #7	$22.81	13.279%	$25.8389	$25.84	$25.85	$25.80
7 purchase totals =	$856.27		$935.7938	$935.80	$935.80	$935.60