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	$67.27	7.302%	$72.1821	$72.18	$72.20	$72.20
Purchase #2	$82.31	9.838%	$90.4077	$90.41	$90.40	$90.40
Purchase #3	$44.65	3.836%	$46.3628	$46.36	$46.35	$46.40
Purchase #4	$192.46	10.850%	$213.3419	$213.34	$213.35	$213.30
Purchase #5	$43.83	6.604%	$46.7245	$46.72	$46.70	$46.70
Purchase #6	$82.83	12.269%	$92.9924	$92.99	$93.00	$93.00
Purchase #7	$196.80	4.817%	$206.2799	$206.28	$206.30	$206.30
7 purchase totals =	$710.15		$768.2913	$768.28	$768.30	$768.30