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	$200.94	12.173%	$225.4004	$225.40	$225.40	$225.40
Purchase #2	$96.34	3.624%	$99.8314	$99.83	$99.85	$99.80
Purchase #3	$181.55	4.812%	$190.2862	$190.29	$190.30	$190.30
Purchase #4	$16.56	8.646%	$17.9918	$17.99	$18.00	$18.00
Purchase #5	$98.72	11.365%	$109.9395	$109.94	$109.95	$109.90
Purchase #6	$31.49	13.140%	$35.6278	$35.63	$35.65	$35.60
Purchase #7	$198.95	12.294%	$223.4089	$223.41	$223.40	$223.40
7 purchase totals =	$824.55		$902.4860	$902.49	$902.55	$902.40