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	$136.28	5.341%	$143.5587	$143.56	$143.55	$143.60
Purchase #2	$82.43	9.522%	$90.279	$90.28	$90.30	$90.30
Purchase #3	$53.98	6.560%	$57.5211	$57.52	$57.50	$57.50
Purchase #4	$195.86	8.843%	$213.1799	$213.18	$213.20	$213.20
Purchase #5	$112.71	11.653%	$125.8441	$125.84	$125.85	$125.80
Purchase #6	$90.54	13.139%	$102.4361	$102.44	$102.45	$102.40
Purchase #7	$41.82	8.407%	$45.3358	$45.34	$45.35	$45.30
7 purchase totals =	$713.62		$778.1547	$778.16	$778.20	$778.10