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	$79.61	3.469%	$82.3717	$82.37	$82.35	$82.40
Purchase #2	$44.38	6.866%	$47.4271	$47.43	$47.45	$47.40
Purchase #3	$35.42	4.109%	$36.8754	$36.88	$36.90	$36.90
Purchase #4	$58.61	5.415%	$61.7837	$61.78	$61.80	$61.80
Purchase #5	$38.66	10.373%	$42.6702	$42.67	$42.65	$42.70
Purchase #6	$109.26	5.307%	$115.0584	$115.06	$115.05	$115.10
Purchase #7	$32.99	8.839%	$35.906	$35.91	$35.90	$35.90
7 purchase totals =	$398.93		$422.0925	$422.10	$422.10	$422.20