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	$28.83	11.529%	$32.1538	$32.15	$32.15	$32.20
Purchase #2	$125.63	13.714%	$142.8589	$142.86	$142.85	$142.90
Purchase #3	$86.73	7.728%	$93.4325	$93.43	$93.45	$93.40
Purchase #4	$79.71	4.564%	$83.348	$83.35	$83.35	$83.30
Purchase #5	$167.46	10.765%	$185.4871	$185.49	$185.50	$185.50
Purchase #6	$153.37	9.722%	$168.2806	$168.28	$168.30	$168.30
Purchase #7	$61.25	5.362%	$64.5342	$64.53	$64.55	$64.50
7 purchase totals =	$702.98		$770.0951	$770.09	$770.15	$770.10