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	$85.31	6.741%	$91.0607	$91.06	$91.05	$91.10
Purchase #2	$86.41	5.731%	$91.3622	$91.36	$91.35	$91.40
Purchase #3	$129.43	11.600%	$144.4439	$144.44	$144.45	$144.40
Purchase #4	$179.75	6.403%	$191.2594	$191.26	$191.25	$191.30
Purchase #5	$119.49	12.807%	$134.7931	$134.79	$134.80	$134.80
Purchase #6	$249.50	12.329%	$280.2609	$280.26	$280.25	$280.30
Purchase #7	$199.54	9.278%	$218.0533	$218.05	$218.05	$218.10
7 purchase totals =	$1,049.43		$1,151.2335	$1,151.22	$1,151.20	$1,151.40