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	$84.33	7.723%	$90.8428	$90.84	$90.85	$90.80
Purchase #2	$245.99	12.224%	$276.0598	$276.06	$276.05	$276.10
Purchase #3	$38.89	5.196%	$40.9107	$40.91	$40.90	$40.90
Purchase #4	$165.37	6.364%	$175.8941	$175.89	$175.90	$175.90
Purchase #5	$237.86	7.276%	$255.1667	$255.17	$255.15	$255.20
Purchase #6	$87.94	12.510%	$98.9413	$98.94	$98.95	$98.90
Purchase #7	$20.39	12.663%	$22.972	$22.97	$22.95	$23.00
7 purchase totals =	$880.77		$960.7874	$960.78	$960.75	$960.80