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	$239.40	3.177%	$247.0057	$247.01	$247.00	$247.00
Purchase #2	$151.38	10.413%	$167.1432	$167.14	$167.15	$167.10
Purchase #3	$81.31	12.299%	$91.3103	$91.31	$91.30	$91.30
Purchase #4	$50.64	8.695%	$55.0431	$55.04	$55.05	$55.00
Purchase #5	$165.27	10.381%	$182.4267	$182.43	$182.45	$182.40
Purchase #6	$64.60	10.439%	$71.3436	$71.34	$71.35	$71.30
Purchase #7	$24.29	12.456%	$27.3156	$27.32	$27.30	$27.30
7 purchase totals =	$776.89		$841.5882	$841.59	$841.60	$841.40