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	$206.63	6.353%	$219.7572	$219.76	$219.75	$219.80
Purchase #2	$67.88	5.315%	$71.4878	$71.49	$71.50	$71.50
Purchase #3	$85.45	8.146%	$92.4108	$92.41	$92.40	$92.40
Purchase #4	$219.74	8.739%	$238.9431	$238.94	$238.95	$238.90
Purchase #5	$186.54	3.182%	$192.4757	$192.48	$192.50	$192.50
Purchase #6	$187.55	3.358%	$193.8479	$193.85	$193.85	$193.80
Purchase #7	$75.51	3.203%	$77.9286	$77.93	$77.95	$77.90
7 purchase totals =	$1,029.30		$1,086.8511	$1,086.86	$1,086.90	$1,086.80