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	$41.70	9.111%	$45.4993	$45.50	$45.50	$45.50
Purchase #2	$168.68	8.410%	$182.866	$182.87	$182.85	$182.90
Purchase #3	$106.26	7.195%	$113.9054	$113.91	$113.90	$113.90
Purchase #4	$176.87	10.208%	$194.9249	$194.92	$194.90	$194.90
Purchase #5	$194.90	8.454%	$211.3768	$211.38	$211.40	$211.40
Purchase #6	$123.91	3.155%	$127.8194	$127.82	$127.80	$127.80
Purchase #7	$152.50	7.745%	$164.3111	$164.31	$164.30	$164.30
7 purchase totals =	$964.82		$1,040.7029	$1,040.71	$1,040.65	$1,040.70