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	$144.36	6.320%	$153.4836	$153.48	$153.50	$153.50
Purchase #2	$149.76	12.341%	$168.2419	$168.24	$168.25	$168.20
Purchase #3	$226.65	10.338%	$250.0811	$250.08	$250.10	$250.10
Purchase #4	$152.60	12.460%	$171.614	$171.61	$171.60	$171.60
Purchase #5	$20.62	9.852%	$22.6515	$22.65	$22.65	$22.70
Purchase #6	$30.78	6.421%	$32.7564	$32.76	$32.75	$32.80
Purchase #7	$62.96	7.290%	$67.5498	$67.55	$67.55	$67.50
7 purchase totals =	$787.73		$866.3783	$866.37	$866.40	$866.40