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	$79.94	3.564%	$82.7891	$82.79	$82.80	$82.80
Purchase #2	$75.87	8.294%	$82.1627	$82.16	$82.15	$82.20
Purchase #3	$160.40	3.393%	$165.8424	$165.84	$165.85	$165.80
Purchase #4	$61.59	4.502%	$64.3628	$64.36	$64.35	$64.40
Purchase #5	$72.65	9.174%	$79.3149	$79.31	$79.30	$79.30
Purchase #6	$165.40	8.416%	$179.3201	$179.32	$179.30	$179.30
Purchase #7	$250.66	13.626%	$284.8149	$284.81	$284.80	$284.80
7 purchase totals =	$866.51		$938.6069	$938.59	$938.55	$938.60