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	$133.80	3.480%	$138.4562	$138.46	$138.45	$138.50
Purchase #2	$176.80	5.685%	$186.8511	$186.85	$186.85	$186.90
Purchase #3	$89.72	13.188%	$101.5523	$101.55	$101.55	$101.60
Purchase #4	$164.31	11.510%	$183.2221	$183.22	$183.20	$183.20
Purchase #5	$99.77	3.468%	$103.23	$103.23	$103.25	$103.20
Purchase #6	$55.39	5.532%	$58.4542	$58.45	$58.45	$58.50
Purchase #7	$221.32	12.311%	$248.5667	$248.57	$248.55	$248.60
7 purchase totals =	$941.11		$1,020.3326	$1,020.33	$1,020.30	$1,020.50