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	$156.84	8.800%	$170.6419	$170.64	$170.65	$170.60
Purchase #2	$47.63	11.594%	$53.1522	$53.15	$53.15	$53.20
Purchase #3	$77.77	9.419%	$85.0952	$85.10	$85.10	$85.10
Purchase #4	$174.78	9.749%	$191.8193	$191.82	$191.80	$191.80
Purchase #5	$160.72	4.507%	$167.9637	$167.96	$167.95	$168.00
Purchase #6	$43.56	3.607%	$45.1312	$45.13	$45.15	$45.10
Purchase #7	$184.66	3.328%	$190.8055	$190.81	$190.80	$190.80
7 purchase totals =	$845.96		$904.6090	$904.61	$904.60	$904.60