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	$54.93	8.796%	$59.7616	$59.76	$59.75	$59.80
Purchase #2	$84.53	6.234%	$89.7996	$89.80	$89.80	$89.80
Purchase #3	$127.35	7.402%	$136.7764	$136.78	$136.80	$136.80
Purchase #4	$183.84	11.215%	$204.4577	$204.46	$204.45	$204.50
Purchase #5	$186.32	9.681%	$204.3576	$204.36	$204.35	$204.40
Purchase #6	$12.27	4.344%	$12.803	$12.80	$12.80	$12.80
Purchase #7	$59.95	3.254%	$61.9008	$61.90	$61.90	$61.90
7 purchase totals =	$709.19		$769.8567	$769.86	$769.85	$770.00