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	$155.61	9.114%	$169.7923	$169.79	$169.80	$169.80
Purchase #2	$102.55	5.351%	$108.0375	$108.04	$108.05	$108.00
Purchase #3	$249.48	11.853%	$279.0509	$279.05	$279.05	$279.10
Purchase #4	$147.48	12.164%	$165.4195	$165.42	$165.40	$165.40
Purchase #5	$241.40	11.540%	$269.2576	$269.26	$269.25	$269.30
Purchase #6	$79.37	3.711%	$82.3154	$82.32	$82.30	$82.30
Purchase #7	$25.81	6.655%	$27.5277	$27.53	$27.55	$27.50
7 purchase totals =	$1,001.70		$1,101.4009	$1,101.41	$1,101.40	$1,101.40