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	$245.36	10.498%	$271.1179	$271.12	$271.10	$271.10
Purchase #2	$118.34	7.333%	$127.0179	$127.02	$127.00	$127.00
Purchase #3	$232.44	4.776%	$243.5413	$243.54	$243.55	$243.50
Purchase #4	$108.42	3.541%	$112.2592	$112.26	$112.25	$112.30
Purchase #5	$22.33	13.407%	$25.3238	$25.32	$25.30	$25.30
Purchase #6	$113.90	13.563%	$129.3483	$129.35	$129.35	$129.30
Purchase #7	$69.61	12.740%	$78.4783	$78.48	$78.50	$78.50
7 purchase totals =	$910.40		$987.0867	$987.09	$987.05	$987.00