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	$66.58	7.574%	$71.6228	$71.62	$71.60	$71.60
Purchase #2	$138.85	4.726%	$145.4121	$145.41	$145.40	$145.40
Purchase #3	$41.52	12.161%	$46.5692	$46.57	$46.55	$46.60
Purchase #4	$168.73	12.559%	$189.9208	$189.92	$189.90	$189.90
Purchase #5	$50.88	9.744%	$55.8377	$55.84	$55.85	$55.80
Purchase #6	$42.52	7.190%	$45.5772	$45.58	$45.60	$45.60
Purchase #7	$119.76	12.566%	$134.809	$134.81	$134.80	$134.80
7 purchase totals =	$628.84		$689.7488	$689.75	$689.70	$689.70