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	$170.37	12.356%	$191.4209	$191.42	$191.40	$191.40
Purchase #2	$89.35	5.614%	$94.3661	$94.37	$94.35	$94.40
Purchase #3	$73.43	11.464%	$81.848	$81.85	$81.85	$81.80
Purchase #4	$74.53	8.406%	$80.795	$80.80	$80.80	$80.80
Purchase #5	$7.44	5.820%	$7.873	$7.87	$7.85	$7.90
Purchase #6	$142.33	5.725%	$150.4784	$150.48	$150.50	$150.50
Purchase #7	$136.78	3.318%	$141.3184	$141.32	$141.30	$141.30
7 purchase totals =	$694.23		$748.0998	$748.11	$748.05	$748.10