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	$242.69	9.313%	$265.2917	$265.29	$265.30	$265.30
Purchase #2	$174.91	12.369%	$196.5446	$196.54	$196.55	$196.50
Purchase #3	$237.65	11.223%	$264.3215	$264.32	$264.30	$264.30
Purchase #4	$239.77	12.515%	$269.7772	$269.78	$269.80	$269.80
Purchase #5	$125.57	6.841%	$134.1602	$134.16	$134.15	$134.20
Purchase #6	$5.78	7.263%	$6.1998	$6.20	$6.20	$6.20
Purchase #7	$46.86	12.479%	$52.7077	$52.71	$52.70	$52.70
7 purchase totals =	$1,073.23		$1,189.0027	$1,189.00	$1,189.00	$1,189.00