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	$60.73	11.270%	$67.5743	$67.57	$67.55	$67.60
Purchase #2	$131.93	9.535%	$144.5095	$144.51	$144.50	$144.50
Purchase #3	$105.48	9.533%	$115.5354	$115.54	$115.55	$115.50
Purchase #4	$78.61	8.180%	$85.0403	$85.04	$85.05	$85.00
Purchase #5	$122.80	9.390%	$134.3309	$134.33	$134.35	$134.30
Purchase #6	$7.32	4.418%	$7.6434	$7.64	$7.65	$7.60
Purchase #7	$135.42	6.439%	$144.1397	$144.14	$144.15	$144.10
7 purchase totals =	$642.29		$698.7735	$698.77	$698.80	$698.60