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	$79.56	7.768%	$85.7402	$85.74	$85.75	$85.70
Purchase #2	$86.86	3.866%	$90.218	$90.22	$90.20	$90.20
Purchase #3	$38.93	9.822%	$42.7537	$42.75	$42.75	$42.80
Purchase #4	$7.76	8.268%	$8.4016	$8.40	$8.40	$8.40
Purchase #5	$129.89	7.527%	$139.6668	$139.67	$139.65	$139.70
Purchase #6	$71.49	9.297%	$78.1364	$78.14	$78.15	$78.10
Purchase #7	$131.59	8.417%	$142.6659	$142.67	$142.65	$142.70
7 purchase totals =	$546.08		$587.5826	$587.59	$587.55	$587.60