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	$234.54	4.801%	$245.8003	$245.80	$245.80	$245.80
Purchase #2	$189.45	12.606%	$213.3321	$213.33	$213.35	$213.30
Purchase #3	$210.34	13.366%	$238.454	$238.45	$238.45	$238.50
Purchase #4	$168.74	10.176%	$185.911	$185.91	$185.90	$185.90
Purchase #5	$230.38	5.756%	$243.6407	$243.64	$243.65	$243.60
Purchase #6	$57.55	7.736%	$62.0021	$62.00	$62.00	$62.00
Purchase #7	$89.54	13.422%	$101.5581	$101.56	$101.55	$101.60
7 purchase totals =	$1,180.54		$1,290.6983	$1,290.69	$1,290.70	$1,290.70