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	$33.39	7.502%	$35.8949	$35.89	$35.90	$35.90
Purchase #2	$216.54	7.806%	$233.4431	$233.44	$233.45	$233.40
Purchase #3	$191.77	12.721%	$216.1651	$216.17	$216.15	$216.20
Purchase #4	$90.98	6.693%	$97.0693	$97.07	$97.05	$97.10
Purchase #5	$188.55	6.568%	$200.934	$200.93	$200.95	$200.90
Purchase #6	$79.97	13.202%	$90.5276	$90.53	$90.55	$90.50
Purchase #7	$49.30	7.818%	$53.1543	$53.15	$53.15	$53.20
7 purchase totals =	$850.50		$927.1883	$927.18	$927.20	$927.20