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	$36.87	6.165%	$39.143	$39.14	$39.15	$39.10
Purchase #2	$243.44	13.548%	$276.4213	$276.42	$276.40	$276.40
Purchase #3	$38.33	4.754%	$40.1522	$40.15	$40.15	$40.20
Purchase #4	$91.61	12.839%	$103.3718	$103.37	$103.35	$103.40
Purchase #5	$198.54	10.538%	$219.4621	$219.46	$219.45	$219.50
Purchase #6	$159.56	5.810%	$168.8304	$168.83	$168.85	$168.80
Purchase #7	$166.81	9.565%	$182.7654	$182.77	$182.75	$182.80
7 purchase totals =	$935.16		$1,030.1462	$1,030.14	$1,030.10	$1,030.20