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	$71.76	11.719%	$80.1696	$80.17	$80.15	$80.20
Purchase #2	$177.32	4.650%	$185.5654	$185.57	$185.55	$185.60
Purchase #3	$64.48	3.864%	$66.9715	$66.97	$66.95	$67.00
Purchase #4	$92.36	6.423%	$98.2923	$98.29	$98.30	$98.30
Purchase #5	$155.67	3.262%	$160.748	$160.75	$160.75	$160.70
Purchase #6	$118.50	4.168%	$123.4391	$123.44	$123.45	$123.40
Purchase #7	$105.82	6.550%	$112.7512	$112.75	$112.75	$112.80
7 purchase totals =	$785.91		$827.9371	$827.94	$827.90	$828.00