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	$242.76	13.404%	$275.2996	$275.30	$275.30	$275.30
Purchase #2	$201.31	11.640%	$224.7425	$224.74	$224.75	$224.70
Purchase #3	$55.94	5.647%	$59.0989	$59.10	$59.10	$59.10
Purchase #4	$220.38	12.598%	$248.1435	$248.14	$248.15	$248.10
Purchase #5	$77.71	10.545%	$85.9045	$85.90	$85.90	$85.90
Purchase #6	$152.45	10.270%	$168.1066	$168.11	$168.10	$168.10
Purchase #7	$156.33	9.290%	$170.8531	$170.85	$170.85	$170.90
7 purchase totals =	$1,106.88		$1,232.1487	$1,232.14	$1,232.15	$1,232.10