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	$164.33	4.255%	$171.3222	$171.32	$171.30	$171.30
Purchase #2	$240.83	9.643%	$264.0532	$264.05	$264.05	$264.10
Purchase #3	$35.99	13.562%	$40.871	$40.87	$40.85	$40.90
Purchase #4	$45.36	9.148%	$49.5095	$49.51	$49.50	$49.50
Purchase #5	$170.80	10.688%	$189.0551	$189.06	$189.05	$189.10
Purchase #6	$30.36	8.284%	$32.875	$32.88	$32.90	$32.90
Purchase #7	$165.90	3.559%	$171.8044	$171.80	$171.80	$171.80
7 purchase totals =	$853.57		$919.4904	$919.49	$919.45	$919.60