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	$49.55	11.192%	$55.0956	$55.10	$55.10	$55.10
Purchase #2	$178.92	11.376%	$199.2739	$199.27	$199.25	$199.30
Purchase #3	$164.41	10.575%	$181.7964	$181.80	$181.80	$181.80
Purchase #4	$117.52	11.872%	$131.472	$131.47	$131.45	$131.50
Purchase #5	$37.64	5.643%	$39.764	$39.76	$39.75	$39.80
Purchase #6	$37.67	6.735%	$40.2071	$40.21	$40.20	$40.20
Purchase #7	$80.59	10.581%	$89.1172	$89.12	$89.10	$89.10
7 purchase totals =	$666.30		$736.7262	$736.73	$736.65	$736.80