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	$131.50	9.759%	$144.3331	$144.33	$144.35	$144.30
Purchase #2	$156.59	6.178%	$166.2641	$166.26	$166.25	$166.30
Purchase #3	$145.46	6.363%	$154.7156	$154.72	$154.70	$154.70
Purchase #4	$218.62	8.564%	$237.3426	$237.34	$237.35	$237.30
Purchase #5	$139.98	5.256%	$147.3373	$147.34	$147.35	$147.30
Purchase #6	$71.95	6.157%	$76.38	$76.38	$76.40	$76.40
Purchase #7	$57.90	3.486%	$59.9184	$59.92	$59.90	$59.90
7 purchase totals =	$922.00		$986.2911	$986.29	$986.30	$986.20