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	$42.58	4.190%	$44.3641	$44.36	$44.35	$44.40
Purchase #2	$245.87	8.752%	$267.3885	$267.39	$267.40	$267.40
Purchase #3	$84.73	5.672%	$89.5359	$89.54	$89.55	$89.50
Purchase #4	$58.90	9.796%	$64.6698	$64.67	$64.65	$64.70
Purchase #5	$103.25	4.746%	$108.1502	$108.15	$108.15	$108.20
Purchase #6	$34.70	7.594%	$37.3351	$37.34	$37.35	$37.30
Purchase #7	$45.78	6.801%	$48.8935	$48.89	$48.90	$48.90
7 purchase totals =	$615.81		$660.3371	$660.34	$660.35	$660.40