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	$108.39	13.776%	$123.3218	$123.32	$123.30	$123.30
Purchase #2	$126.28	11.835%	$141.2252	$141.23	$141.25	$141.20
Purchase #3	$171.86	11.467%	$191.5672	$191.57	$191.55	$191.60
Purchase #4	$225.31	4.552%	$235.5661	$235.57	$235.55	$235.60
Purchase #5	$55.25	5.595%	$58.3412	$58.34	$58.35	$58.30
Purchase #6	$120.52	5.274%	$126.8762	$126.88	$126.90	$126.90
Purchase #7	$191.74	9.396%	$209.7559	$209.76	$209.75	$209.80
7 purchase totals =	$999.35		$1,086.6536	$1,086.67	$1,086.65	$1,086.70