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	$37.52	12.134%	$42.0727	$42.07	$42.05	$42.10
Purchase #2	$128.84	6.404%	$137.0909	$137.09	$137.10	$137.10
Purchase #3	$190.38	10.124%	$209.6541	$209.65	$209.65	$209.70
Purchase #4	$53.29	10.871%	$59.0832	$59.08	$59.10	$59.10
Purchase #5	$134.29	10.338%	$148.1729	$148.17	$148.15	$148.20
Purchase #6	$57.74	12.686%	$65.0649	$65.06	$65.05	$65.10
Purchase #7	$28.84	11.498%	$32.156	$32.16	$32.15	$32.20
7 purchase totals =	$630.90		$693.2947	$693.28	$693.25	$693.50