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	$78.87	13.664%	$89.6468	$89.65	$89.65	$89.60
Purchase #2	$100.80	9.252%	$110.126	$110.13	$110.15	$110.10
Purchase #3	$17.62	5.275%	$18.5495	$18.55	$18.55	$18.50
Purchase #4	$119.69	3.860%	$124.31	$124.31	$124.30	$124.30
Purchase #5	$105.80	11.273%	$117.7268	$117.73	$117.75	$117.70
Purchase #6	$190.96	4.414%	$199.389	$199.39	$199.40	$199.40
Purchase #7	$29.90	12.794%	$33.7254	$33.73	$33.75	$33.70
7 purchase totals =	$643.64		$693.4735	$693.49	$693.55	$693.30