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	$246.25	11.424%	$274.3816	$274.38	$274.40	$274.40
Purchase #2	$220.36	13.534%	$250.1835	$250.18	$250.20	$250.20
Purchase #3	$85.32	5.602%	$90.0996	$90.10	$90.10	$90.10
Purchase #4	$131.61	5.514%	$138.867	$138.87	$138.85	$138.90
Purchase #5	$19.64	6.331%	$20.8834	$20.88	$20.90	$20.90
Purchase #6	$136.69	4.510%	$142.8547	$142.85	$142.85	$142.90
Purchase #7	$244.94	11.357%	$272.7578	$272.76	$272.75	$272.80
7 purchase totals =	$1,084.81		$1,190.0276	$1,190.02	$1,190.05	$1,190.20