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	$24.94	7.367%	$26.7773	$26.78	$26.80	$26.80
Purchase #2	$174.76	12.495%	$196.5963	$196.60	$196.60	$196.60
Purchase #3	$200.75	11.386%	$223.6074	$223.61	$223.60	$223.60
Purchase #4	$235.64	13.818%	$268.2007	$268.20	$268.20	$268.20
Purchase #5	$18.25	11.270%	$20.3068	$20.31	$20.30	$20.30
Purchase #6	$96.96	7.575%	$104.3047	$104.30	$104.30	$104.30
Purchase #7	$51.98	10.711%	$57.5476	$57.55	$57.55	$57.50
7 purchase totals =	$803.28		$897.3408	$897.35	$897.35	$897.30