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	$128.38	9.485%	$140.5568	$140.56	$140.55	$140.60
Purchase #2	$124.65	12.362%	$140.0592	$140.06	$140.05	$140.10
Purchase #3	$18.35	10.242%	$20.2294	$20.23	$20.25	$20.20
Purchase #4	$65.61	3.286%	$67.7659	$67.77	$67.75	$67.80
Purchase #5	$92.42	7.212%	$99.0853	$99.09	$99.10	$99.10
Purchase #6	$191.83	4.279%	$200.0384	$200.04	$200.05	$200.00
Purchase #7	$168.71	3.127%	$173.9856	$173.99	$174.00	$174.00
7 purchase totals =	$789.95		$841.7206	$841.74	$841.75	$841.80