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	$67.77	8.404%	$73.4654	$73.47	$73.45	$73.50
Purchase #2	$184.28	4.493%	$192.5597	$192.56	$192.55	$192.60
Purchase #3	$227.46	8.120%	$245.9298	$245.93	$245.95	$245.90
Purchase #4	$174.57	12.372%	$196.1678	$196.17	$196.15	$196.20
Purchase #5	$99.27	9.757%	$108.9558	$108.96	$108.95	$109.00
Purchase #6	$70.47	3.360%	$72.8378	$72.84	$72.85	$72.80
Purchase #7	$37.45	6.311%	$39.8135	$39.81	$39.80	$39.80
7 purchase totals =	$861.27		$929.7298	$929.74	$929.70	$929.80