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	$249.95	6.218%	$265.4919	$265.49	$265.50	$265.50
Purchase #2	$86.87	7.498%	$93.3835	$93.38	$93.40	$93.40
Purchase #3	$85.34	4.625%	$89.287	$89.29	$89.30	$89.30
Purchase #4	$58.58	6.421%	$62.3414	$62.34	$62.35	$62.30
Purchase #5	$100.68	13.799%	$114.5728	$114.57	$114.55	$114.60
Purchase #6	$225.33	9.761%	$247.3245	$247.32	$247.30	$247.30
Purchase #7	$101.61	4.457%	$106.1388	$106.14	$106.15	$106.10
7 purchase totals =	$908.36		$978.5399	$978.53	$978.55	$978.50