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	$77.74	12.412%	$87.3891	$87.39	$87.40	$87.40
Purchase #2	$137.42	8.647%	$149.3027	$149.30	$149.30	$149.30
Purchase #3	$222.80	6.834%	$238.0262	$238.03	$238.05	$238.00
Purchase #4	$155.73	4.624%	$162.931	$162.93	$162.95	$162.90
Purchase #5	$81.42	12.236%	$91.3826	$91.38	$91.40	$91.40
Purchase #6	$219.38	3.496%	$227.0495	$227.05	$227.05	$227.00
Purchase #7	$53.96	10.479%	$59.6145	$59.61	$59.60	$59.60
7 purchase totals =	$948.45		$1,015.6956	$1,015.69	$1,015.75	$1,015.60