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	$155.56	5.873%	$164.696	$164.70	$164.70	$164.70
Purchase #2	$220.31	13.772%	$250.6511	$250.65	$250.65	$250.70
Purchase #3	$68.60	6.871%	$73.3135	$73.31	$73.30	$73.30
Purchase #4	$38.36	5.649%	$40.527	$40.53	$40.55	$40.50
Purchase #5	$68.51	5.778%	$72.4685	$72.47	$72.45	$72.50
Purchase #6	$218.83	12.315%	$245.7789	$245.78	$245.80	$245.80
Purchase #7	$32.48	3.218%	$33.5252	$33.53	$33.55	$33.50
7 purchase totals =	$802.65		$880.9602	$880.97	$881.00	$881.00