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	$37.82	7.484%	$40.6504	$40.65	$40.65	$40.70
Purchase #2	$39.83	12.841%	$44.9446	$44.94	$44.95	$44.90
Purchase #3	$156.96	11.153%	$174.4657	$174.47	$174.45	$174.50
Purchase #4	$194.55	10.217%	$214.4272	$214.43	$214.45	$214.40
Purchase #5	$172.80	7.209%	$185.2572	$185.26	$185.25	$185.30
Purchase #6	$108.93	8.424%	$118.1063	$118.11	$118.10	$118.10
Purchase #7	$209.41	6.807%	$223.6645	$223.66	$223.65	$223.70
7 purchase totals =	$920.30		$1,001.5159	$1,001.52	$1,001.50	$1,001.60