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	$68.35	5.498%	$72.1079	$72.11	$72.10	$72.10
Purchase #2	$103.99	5.634%	$109.8488	$109.85	$109.85	$109.80
Purchase #3	$132.80	5.685%	$140.3497	$140.35	$140.35	$140.30
Purchase #4	$49.48	7.484%	$53.1831	$53.18	$53.20	$53.20
Purchase #5	$37.95	3.582%	$39.3094	$39.31	$39.30	$39.30
Purchase #6	$66.68	9.185%	$72.8046	$72.80	$72.80	$72.80
Purchase #7	$79.43	12.501%	$89.3595	$89.36	$89.35	$89.40
7 purchase totals =	$538.68		$576.9630	$576.96	$576.95	$576.90