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	$37.72	5.433%	$39.7693	$39.77	$39.75	$39.80
Purchase #2	$176.71	5.599%	$186.604	$186.60	$186.60	$186.60
Purchase #3	$81.47	8.217%	$88.1644	$88.16	$88.15	$88.20
Purchase #4	$28.78	12.252%	$32.3061	$32.31	$32.30	$32.30
Purchase #5	$232.59	5.592%	$245.5964	$245.60	$245.60	$245.60
Purchase #6	$83.90	3.873%	$87.1494	$87.15	$87.15	$87.10
Purchase #7	$84.52	5.785%	$89.4095	$89.41	$89.40	$89.40
7 purchase totals =	$725.69		$768.9991	$769.00	$768.95	$769.00