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	$171.56	8.610%	$186.3313	$186.33	$186.35	$186.30
Purchase #2	$79.60	3.777%	$82.6065	$82.61	$82.60	$82.60
Purchase #3	$164.75	10.314%	$181.7423	$181.74	$181.75	$181.70
Purchase #4	$212.90	7.782%	$229.4679	$229.47	$229.45	$229.50
Purchase #5	$39.68	9.235%	$43.3444	$43.34	$43.35	$43.30
Purchase #6	$82.54	8.135%	$89.2546	$89.25	$89.25	$89.30
Purchase #7	$176.28	4.166%	$183.6238	$183.62	$183.60	$183.60
7 purchase totals =	$927.31		$996.3708	$996.36	$996.35	$996.30