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	$31.84	11.441%	$35.4828	$35.48	$35.50	$35.50
Purchase #2	$239.39	10.297%	$264.04	$264.04	$264.05	$264.00
Purchase #3	$114.50	11.211%	$127.3366	$127.34	$127.35	$127.30
Purchase #4	$58.61	10.384%	$64.6961	$64.70	$64.70	$64.70
Purchase #5	$167.56	7.365%	$179.9008	$179.90	$179.90	$179.90
Purchase #6	$52.73	13.113%	$59.6445	$59.64	$59.65	$59.60
Purchase #7	$237.96	11.710%	$265.8251	$265.83	$265.85	$265.80
7 purchase totals =	$902.59		$996.9259	$996.93	$997.00	$996.80