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	$92.55	13.641%	$105.1747	$105.17	$105.15	$105.20
Purchase #2	$247.74	4.625%	$259.198	$259.20	$259.20	$259.20
Purchase #3	$41.44	9.279%	$45.2852	$45.29	$45.30	$45.30
Purchase #4	$53.47	10.746%	$59.2159	$59.22	$59.20	$59.20
Purchase #5	$168.86	7.405%	$181.3641	$181.36	$181.35	$181.40
Purchase #6	$120.31	12.762%	$135.664	$135.66	$135.65	$135.70
Purchase #7	$81.54	4.710%	$85.3805	$85.38	$85.40	$85.40
7 purchase totals =	$805.91		$871.2824	$871.28	$871.25	$871.40