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	$122.48	4.254%	$127.6903	$127.69	$127.70	$127.70
Purchase #2	$113.91	12.463%	$128.1066	$128.11	$128.10	$128.10
Purchase #3	$78.76	10.365%	$86.9235	$86.92	$86.90	$86.90
Purchase #4	$106.47	3.787%	$110.502	$110.50	$110.50	$110.50
Purchase #5	$106.75	4.382%	$111.4278	$111.43	$111.45	$111.40
Purchase #6	$190.26	6.682%	$202.9732	$202.97	$202.95	$203.00
Purchase #7	$79.64	3.464%	$82.3987	$82.40	$82.40	$82.40
7 purchase totals =	$798.27		$850.0221	$850.02	$850.00	$850.00