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	$6.81	11.772%	$7.6117	$7.61	$7.60	$7.60
Purchase #2	$205.64	7.261%	$220.5715	$220.57	$220.55	$220.60
Purchase #3	$79.43	12.423%	$89.2976	$89.30	$89.30	$89.30
Purchase #4	$169.86	3.323%	$175.5044	$175.50	$175.50	$175.50
Purchase #5	$50.75	4.774%	$53.1728	$53.17	$53.15	$53.20
Purchase #6	$79.81	6.864%	$85.2882	$85.29	$85.30	$85.30
Purchase #7	$181.29	5.792%	$191.7903	$191.79	$191.80	$191.80
7 purchase totals =	$773.59		$823.2365	$823.23	$823.20	$823.30