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	$70.32	11.163%	$78.1698	$78.17	$78.15	$78.20
Purchase #2	$79.34	6.113%	$84.1901	$84.19	$84.20	$84.20
Purchase #3	$25.37	12.606%	$28.5681	$28.57	$28.55	$28.60
Purchase #4	$50.90	10.754%	$56.3738	$56.37	$56.35	$56.40
Purchase #5	$96.76	13.576%	$109.8961	$109.90	$109.90	$109.90
Purchase #6	$243.27	12.354%	$273.3236	$273.32	$273.30	$273.30
Purchase #7	$85.42	4.362%	$89.146	$89.15	$89.15	$89.10
7 purchase totals =	$651.38		$719.6675	$719.67	$719.60	$719.70