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	$35.61	12.227%	$39.964	$39.96	$39.95	$40.00
Purchase #2	$72.86	7.256%	$78.1467	$78.15	$78.15	$78.10
Purchase #3	$143.83	6.522%	$153.2106	$153.21	$153.20	$153.20
Purchase #4	$176.59	12.851%	$199.2836	$199.28	$199.30	$199.30
Purchase #5	$207.36	10.856%	$229.871	$229.87	$229.85	$229.90
Purchase #6	$184.70	5.231%	$194.3617	$194.36	$194.35	$194.40
Purchase #7	$160.26	3.507%	$165.8803	$165.88	$165.90	$165.90
7 purchase totals =	$981.21		$1,060.7179	$1,060.71	$1,060.70	$1,060.80