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	$81.68	9.413%	$89.3685	$89.37	$89.35	$89.40
Purchase #2	$194.27	7.395%	$208.6363	$208.64	$208.65	$208.60
Purchase #3	$42.94	5.765%	$45.4155	$45.42	$45.40	$45.40
Purchase #4	$136.83	4.311%	$142.7287	$142.73	$142.75	$142.70
Purchase #5	$180.35	5.787%	$190.7869	$190.79	$190.80	$190.80
Purchase #6	$180.37	8.649%	$195.9702	$195.97	$195.95	$196.00
Purchase #7	$18.88	10.507%	$20.8637	$20.86	$20.85	$20.90
7 purchase totals =	$835.32		$893.7698	$893.78	$893.75	$893.80