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	$201.50	5.825%	$213.2374	$213.24	$213.25	$213.20
Purchase #2	$148.55	11.392%	$165.4728	$165.47	$165.45	$165.50
Purchase #3	$117.73	5.258%	$123.9202	$123.92	$123.90	$123.90
Purchase #4	$106.46	6.739%	$113.6343	$113.63	$113.65	$113.60
Purchase #5	$86.49	3.848%	$89.8181	$89.82	$89.80	$89.80
Purchase #6	$45.46	11.417%	$50.6502	$50.65	$50.65	$50.70
Purchase #7	$7.63	13.605%	$8.6681	$8.67	$8.65	$8.70
7 purchase totals =	$713.82		$765.4011	$765.40	$765.35	$765.40