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	$240.30	12.190%	$269.5926	$269.59	$269.60	$269.60
Purchase #2	$143.64	11.700%	$160.4459	$160.45	$160.45	$160.40
Purchase #3	$168.33	6.361%	$179.0375	$179.04	$179.05	$179.00
Purchase #4	$238.47	8.550%	$258.8592	$258.86	$258.85	$258.90
Purchase #5	$154.30	8.810%	$167.8938	$167.89	$167.90	$167.90
Purchase #6	$199.31	9.395%	$218.0352	$218.04	$218.05	$218.00
Purchase #7	$222.98	9.772%	$244.7696	$244.77	$244.75	$244.80
7 purchase totals =	$1,367.33		$1,498.6338	$1,498.64	$1,498.65	$1,498.60