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	$126.55	3.554%	$131.0476	$131.05	$131.05	$131.00
Purchase #2	$192.50	11.819%	$215.2516	$215.25	$215.25	$215.30
Purchase #3	$155.84	12.130%	$174.7434	$174.74	$174.75	$174.70
Purchase #4	$187.37	11.557%	$209.0244	$209.02	$209.00	$209.00
Purchase #5	$67.36	7.381%	$72.3318	$72.33	$72.35	$72.30
Purchase #6	$41.57	3.536%	$43.0399	$43.04	$43.05	$43.00
Purchase #7	$29.26	11.667%	$32.6738	$32.67	$32.65	$32.70
7 purchase totals =	$800.45		$878.1125	$878.10	$878.10	$878.00