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	$67.97	6.131%	$72.1372	$72.14	$72.15	$72.10
Purchase #2	$164.75	11.689%	$184.0076	$184.01	$184.00	$184.00
Purchase #3	$150.95	7.431%	$162.1671	$162.17	$162.15	$162.20
Purchase #4	$118.62	13.773%	$134.9575	$134.96	$134.95	$135.00
Purchase #5	$68.55	6.273%	$72.8501	$72.85	$72.85	$72.90
Purchase #6	$97.73	11.672%	$109.137	$109.14	$109.15	$109.10
Purchase #7	$108.76	8.778%	$118.307	$118.31	$118.30	$118.30
7 purchase totals =	$777.33		$853.5635	$853.58	$853.55	$853.60