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	$30.27	6.498%	$32.2369	$32.24	$32.25	$32.20
Purchase #2	$40.93	3.708%	$42.4477	$42.45	$42.45	$42.40
Purchase #3	$176.25	3.284%	$182.0381	$182.04	$182.05	$182.00
Purchase #4	$25.84	8.472%	$28.0292	$28.03	$28.05	$28.00
Purchase #5	$125.77	4.431%	$131.3429	$131.34	$131.35	$131.30
Purchase #6	$95.79	8.220%	$103.6639	$103.66	$103.65	$103.70
Purchase #7	$181.94	4.693%	$190.4784	$190.48	$190.50	$190.50
7 purchase totals =	$676.79		$710.2371	$710.24	$710.30	$710.10