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	$77.37	7.144%	$82.8973	$82.90	$82.90	$82.90
Purchase #2	$98.91	9.119%	$107.9296	$107.93	$107.95	$107.90
Purchase #3	$130.30	8.405%	$141.2517	$141.25	$141.25	$141.30
Purchase #4	$31.85	12.401%	$35.7997	$35.80	$35.80	$35.80
Purchase #5	$135.31	12.335%	$152.0005	$152.00	$152.00	$152.00
Purchase #6	$58.30	4.795%	$61.0955	$61.10	$61.10	$61.10
Purchase #7	$53.86	8.145%	$58.2469	$58.25	$58.25	$58.20
7 purchase totals =	$585.90		$639.2212	$639.23	$639.25	$639.20