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	$38.94	8.809%	$42.3702	$42.37	$42.35	$42.40
Purchase #2	$35.56	6.488%	$37.8671	$37.87	$37.85	$37.90
Purchase #3	$245.27	9.864%	$269.4634	$269.46	$269.45	$269.50
Purchase #4	$77.69	3.172%	$80.1543	$80.15	$80.15	$80.20
Purchase #5	$220.56	12.855%	$248.913	$248.91	$248.90	$248.90
Purchase #6	$167.47	6.816%	$178.8848	$178.88	$178.90	$178.90
Purchase #7	$6.78	6.806%	$7.2414	$7.24	$7.25	$7.20
7 purchase totals =	$792.27		$864.8942	$864.88	$864.85	$865.00