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	$90.43	9.710%	$99.2108	$99.21	$99.20	$99.20
Purchase #2	$178.30	6.182%	$189.3225	$189.32	$189.30	$189.30
Purchase #3	$169.61	10.729%	$187.8075	$187.81	$187.80	$187.80
Purchase #4	$71.59	9.488%	$78.3825	$78.38	$78.40	$78.40
Purchase #5	$61.85	13.596%	$70.2591	$70.26	$70.25	$70.30
Purchase #6	$155.25	8.435%	$168.3453	$168.35	$168.35	$168.30
Purchase #7	$37.86	9.370%	$41.4075	$41.41	$41.40	$41.40
7 purchase totals =	$764.89		$834.7352	$834.74	$834.70	$834.70