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	$29.48	7.127%	$31.581	$31.58	$31.60	$31.60
Purchase #2	$183.88	10.874%	$203.8751	$203.88	$203.90	$203.90
Purchase #3	$167.96	12.311%	$188.6376	$188.64	$188.65	$188.60
Purchase #4	$222.89	4.367%	$232.6236	$232.62	$232.60	$232.60
Purchase #5	$29.86	8.144%	$32.2918	$32.29	$32.30	$32.30
Purchase #6	$204.79	9.348%	$223.9338	$223.93	$223.95	$223.90
Purchase #7	$53.98	10.321%	$59.5513	$59.55	$59.55	$59.60
7 purchase totals =	$892.84		$972.4942	$972.49	$972.55	$972.50