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	$250.30	7.234%	$268.4067	$268.41	$268.40	$268.40
Purchase #2	$240.32	12.601%	$270.6027	$270.60	$270.60	$270.60
Purchase #3	$187.33	4.645%	$196.0315	$196.03	$196.05	$196.00
Purchase #4	$41.93	8.367%	$45.4383	$45.44	$45.45	$45.40
Purchase #5	$31.73	10.785%	$35.1521	$35.15	$35.15	$35.20
Purchase #6	$141.75	3.441%	$146.6276	$146.63	$146.65	$146.60
Purchase #7	$163.60	9.466%	$179.0864	$179.09	$179.10	$179.10
7 purchase totals =	$1,056.96		$1,141.3453	$1,141.35	$1,141.40	$1,141.30