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	$39.78	9.276%	$43.47	$43.47	$43.45	$43.50
Purchase #2	$166.46	10.450%	$183.8551	$183.86	$183.85	$183.90
Purchase #3	$18.27	5.286%	$19.2358	$19.24	$19.25	$19.20
Purchase #4	$56.61	9.351%	$61.9036	$61.90	$61.90	$61.90
Purchase #5	$40.65	12.653%	$45.7934	$45.79	$45.80	$45.80
Purchase #6	$245.46	3.368%	$253.7271	$253.73	$253.75	$253.70
Purchase #7	$182.37	3.814%	$189.3256	$189.33	$189.35	$189.30
7 purchase totals =	$749.60		$797.3106	$797.32	$797.35	$797.30