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	$28.77	9.242%	$31.4289	$31.43	$31.45	$31.40
Purchase #2	$54.78	9.197%	$59.8181	$59.82	$59.80	$59.80
Purchase #3	$69.40	10.123%	$76.4254	$76.43	$76.45	$76.40
Purchase #4	$54.31	3.228%	$56.0631	$56.06	$56.05	$56.10
Purchase #5	$213.84	4.460%	$223.3773	$223.38	$223.40	$223.40
Purchase #6	$85.53	13.383%	$96.9765	$96.98	$97.00	$97.00
Purchase #7	$62.38	7.840%	$67.2706	$67.27	$67.25	$67.30
7 purchase totals =	$569.01		$611.3599	$611.37	$611.40	$611.40