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	$86.86	4.338%	$90.628	$90.63	$90.65	$90.60
Purchase #2	$235.43	5.301%	$247.9101	$247.91	$247.90	$247.90
Purchase #3	$229.37	4.573%	$239.8591	$239.86	$239.85	$239.90
Purchase #4	$170.70	12.398%	$191.8634	$191.86	$191.85	$191.90
Purchase #5	$218.57	5.148%	$229.822	$229.82	$229.80	$229.80
Purchase #6	$250.27	12.837%	$282.3972	$282.40	$282.40	$282.40
Purchase #7	$14.59	6.503%	$15.5388	$15.54	$15.55	$15.50
7 purchase totals =	$1,205.79		$1,298.0186	$1,298.02	$1,298.00	$1,298.00