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	$163.53	6.859%	$174.7465	$174.75	$174.75	$174.70
Purchase #2	$84.96	10.441%	$93.8307	$93.83	$93.85	$93.80
Purchase #3	$47.47	12.348%	$53.3316	$53.33	$53.35	$53.30
Purchase #4	$153.65	13.746%	$174.7707	$174.77	$174.75	$174.80
Purchase #5	$77.54	10.780%	$85.8988	$85.90	$85.90	$85.90
Purchase #6	$68.30	5.438%	$72.0142	$72.01	$72.00	$72.00
Purchase #7	$135.31	11.808%	$151.2874	$151.29	$151.30	$151.30
7 purchase totals =	$730.76		$805.8799	$805.88	$805.90	$805.80