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	$28.85	9.502%	$31.5913	$31.59	$31.60	$31.60
Purchase #2	$110.26	6.680%	$117.6254	$117.63	$117.65	$117.60
Purchase #3	$99.96	9.329%	$109.2853	$109.29	$109.30	$109.30
Purchase #4	$35.89	5.595%	$37.898	$37.90	$37.90	$37.90
Purchase #5	$216.35	10.308%	$238.6514	$238.65	$238.65	$238.70
Purchase #6	$193.81	12.652%	$218.3308	$218.33	$218.35	$218.30
Purchase #7	$133.83	5.685%	$141.4382	$141.44	$141.45	$141.40
7 purchase totals =	$818.95		$894.8204	$894.83	$894.90	$894.80