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	$146.72	10.263%	$161.7779	$161.78	$161.80	$161.80
Purchase #2	$154.40	6.811%	$164.9162	$164.92	$164.90	$164.90
Purchase #3	$216.59	3.204%	$223.5295	$223.53	$223.55	$223.50
Purchase #4	$72.90	7.761%	$78.5578	$78.56	$78.55	$78.60
Purchase #5	$179.88	10.189%	$198.208	$198.21	$198.20	$198.20
Purchase #6	$169.74	12.623%	$191.1663	$191.17	$191.15	$191.20
Purchase #7	$238.40	8.726%	$259.2028	$259.20	$259.20	$259.20
7 purchase totals =	$1,178.63		$1,277.3585	$1,277.37	$1,277.35	$1,277.40