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	$78.37	3.569%	$81.167	$81.17	$81.15	$81.20
Purchase #2	$152.26	12.342%	$171.0519	$171.05	$171.05	$171.10
Purchase #3	$27.55	3.334%	$28.4685	$28.47	$28.45	$28.50
Purchase #4	$142.89	7.411%	$153.4796	$153.48	$153.50	$153.50
Purchase #5	$145.51	3.671%	$150.8517	$150.85	$150.85	$150.90
Purchase #6	$196.54	6.722%	$209.7514	$209.75	$209.75	$209.80
Purchase #7	$173.49	10.532%	$191.762	$191.76	$191.75	$191.80
7 purchase totals =	$916.61		$986.5321	$986.53	$986.50	$986.80