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	$134.91	12.655%	$151.9829	$151.98	$152.00	$152.00
Purchase #2	$52.77	13.376%	$59.8285	$59.83	$59.85	$59.80
Purchase #3	$72.96	10.215%	$80.4129	$80.41	$80.40	$80.40
Purchase #4	$123.38	6.386%	$131.259	$131.26	$131.25	$131.30
Purchase #5	$228.90	13.268%	$259.2705	$259.27	$259.25	$259.30
Purchase #6	$30.56	9.492%	$33.4608	$33.46	$33.45	$33.50
Purchase #7	$193.38	12.419%	$217.3959	$217.40	$217.40	$217.40
7 purchase totals =	$836.86		$933.6105	$933.61	$933.60	$933.70