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	$244.25	11.810%	$273.0959	$273.10	$273.10	$273.10
Purchase #2	$37.43	13.554%	$42.5033	$42.50	$42.50	$42.50
Purchase #3	$28.83	8.124%	$31.1721	$31.17	$31.15	$31.20
Purchase #4	$187.90	13.248%	$212.793	$212.79	$212.80	$212.80
Purchase #5	$115.89	10.411%	$127.9553	$127.96	$127.95	$128.00
Purchase #6	$49.96	12.759%	$56.3344	$56.33	$56.35	$56.30
Purchase #7	$194.96	8.483%	$211.4985	$211.50	$211.50	$211.50
7 purchase totals =	$859.22		$955.3525	$955.35	$955.35	$955.40