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	$31.49	6.675%	$33.592	$33.59	$33.60	$33.60
Purchase #2	$80.83	12.632%	$91.0404	$91.04	$91.05	$91.00
Purchase #3	$12.68	3.523%	$13.1267	$13.13	$13.15	$13.10
Purchase #4	$198.67	12.672%	$223.8455	$223.85	$223.85	$223.80
Purchase #5	$166.60	3.643%	$172.6692	$172.67	$172.65	$172.70
Purchase #6	$130.82	12.560%	$147.251	$147.25	$147.25	$147.30
Purchase #7	$131.49	6.417%	$139.9277	$139.93	$139.95	$139.90
7 purchase totals =	$752.58		$821.4525	$821.46	$821.50	$821.40